Autoregulation of thyroid-specific gene transcription by thyroglobulin

Gene biomarkers for the assessment of thyroid-disrupting activity in zebrafish embryos

Active ingredients of pesticides or biocides and industrial chemicals can negatively affect environmental organisms, potentially endangering populations and ecosystems. European legislation mandates that chemical manufacturers provide data for the environmental risk assessment of substances to obtain registration. Endocrine disruptors, substances that interfere with the hormone system, are not granted marketing authorization due to their adverse effects. Current methods for identifying disruptors targeting the thyroid hormone system are costly and require many amphibians. Consequently, alternative methods compliant with the 3R principle (replacement, reduction, refinement) are essential to prioritize risk assessment using reliable biomarkers at non-protected life stages. Our study focused on detecting robust biomarkers for thyroid-disrupting mechanisms of action (MoA) by analyzing molecular signatures in zebrafish embryos induced by deiodinase inhibitor iopanoic acid and thyroid peroxidase inhibitor methimazole. We exposed freshly fertilized zebrafish eggs to these compounds, measuring lethality, hatching rate, swim bladder size and transcriptomic responses. Both compounds significantly reduced swim bladder size, aligning with prior findings. Transcriptome analysis revealed specific molecular fingerprints consistent with the MoA under investigation. This analysis confirmed regulation directions seen in other studies involving thyroid disruptors and allowed us to identify genes like tg, scl2a11b, guca1d, cthrc1a, si:ch211-226h7.5, soul5, nnt2, cox6a2 and mep1a as biomarker genes for thyroid disrupting MoA in zebrafish embryos as per OECD test guideline 236. Future screening methods based on our findings will enable precise identification of thyroid-related activity in chemicals, promoting the development of environmentally safer substances. Additionally, these biomarkers could potentially be incorporated into legally mandated chronic toxicity tests in fish, potentially replacing amphibian tests for thyroid disruption screening in the future.

Functional variants in a TTTG microsatellite on 15q26.1 cause familial nonautoimmune thyroid abnormalities

Insufficient thyroid hormone production in newborns is referred to as congenital hypothyroidism. Multinodular goiter (MNG), characterized by an enlarged thyroid gland with multiple nodules, is usually seen in adults and is recognized as a separate disorder from congenital hypothyroidism. Here we performed a linkage analysis of a family with both nongoitrous congenital hypothyroidism and MNG and identified a signal at 15q26.1. Follow-up analyses with whole-genome sequencing and genetic screening in congenital hypothyroidism and MNG cohorts showed that changes in a noncoding TTTG microsatellite on 15q26.1 were frequently observed in congenital hypothyroidism (137 in 989) and MNG (3 in 33) compared with controls (3 in 38,722). Characterization of the noncoding variants with epigenomic data and in vitro experiments suggested that the microsatellite is located in a thyroid-specific transcriptional repressor, and its activity is disrupted by the variants. Collectively, we presented genetic evidence linking nongoitrous congenital hypothyroidism and MNG, providing unique insights into thyroid abnormalities.

Role of ST6GAL1 in Thyroid Cancers: Insights from Tissue Analysis and Genomic Datasets

Thyroid cancer is the predominant endocrine-related malignancy. ST6 β-galactoside α2,6-sialyltransferase 1 (ST6GAL1) has been studied in various types of cancers; however, the expression and function of ST6GAL1 in thyroid cancer has not been investigated so far. Previously, we conducted two genome-wide association studies and have identified the association of the ST6GAL1 gene with plasma thyroglobulin (Tg) levels. Since Tg levels are altered in thyroid pathologies, in the current study, we wanted to evaluate the expression of ST6GAL1 in thyroid cancer tissues. We performed an immunohistochemical analysis using human thyroid tissue from 89 patients and analyzed ST6GAL1 protein expression in papillary thyroid cancer (including follicular variant and microcarcinoma) and follicular thyroid cancer in comparison to normal thyroid tissue. Additionally, ST6GAL1 mRNA levels from The Cancer Genome Atlas (TCGA, n = 572) and the Genotype-Tissue Expression (GTEx) project (n = 279) were examined. The immunohistochemical analysis revealed higher ST6GAL1 protein expression in all thyroid tumors compared to normal thyroid tissue. TCGA data revealed increased ST6GAL1 mRNA levels in both primary and metastatic tumors versus controls. Notably, the follicular variant of papillary thyroid cancer exhibited significantly higher ST6GAL1 mRNA levels than classic papillary thyroid cancer. High ST6GAL1 mRNA levels significantly correlated with lymph node metastasis status, clinical stage, and reduced survival rate. ST6GAL1 emerges as a potential cancer-associated glycosyltransferase in thyroid malignancies, offering valuable insights into its diagnostic and prognostic significance.

Expression landscapes in non-small cell lung cancer shaped by the thyroid transcription factor 1

TTF-1-expressing non-small cell lung cancer (NSCLC) is one of the most prevalent lung cancer types worldwide. However, theparadoxical activity of TTF-1 in both lung carcinogenesis and tumor suppression is believed to be context-dependentwhich calls for a deeper understanding about the pathological expression of TTF-1. In addition, the expression circuitry of TTF-1-target genes in NSCLC has not been well examined which necessitates to revisit the involvement of TTF-1- in a multitude of oncologic pathways. We used RNA-seq and clinical data of patients from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx), including ChIP-seq data from different NSCLC cell lines, and mapped the proteome of NSCLC tumor. Our analysis showed significant variability in TTF-1 expression among NSCLC,and further clarified that this variability is orchestrated at the transcriptional level. We also found that high TTF-1 expression could negatively influence the survival outcomes of stage 1 LUAD which may be attributed to growth factor receptor-driven activation of mitogenic and angiogenic pathways. Mechanistically, TTF-1 may also control the genes associated with pathways involved in acquired TKI drug resistance or response to immune checkpoint inhibitors. Lastly, proteome-based biomarker discovery in stage 1 LUAD showed that TTF-1 positivity is potentially associated with the upregulation of several oncogenes which includes interferon proteins, MUC1, STAT3, and EIF2AK2. Collectively, this study highlights the potential involvement of TTF-1 in cell proliferation, immune evasion, and angiogenesis in early-stage NSCLC.

Thyroglobulin regulates the expression and localization of the novel iodide transporter solute carrier family 26 member 7 (SLC26A7) in thyrocytes

Solute carrier family 26 member 7 (SLC26A7), identified as a causative gene for congenital hypothyroidism, was found to be a novel iodide transporter expressed on the apical side of the follicular epithelium of the thyroid. We recently showed that TSH suppressed the expression of SLC26A7 and induces its localization to the plasma membrane, where it functions. We also showed that the ability of TSH to induce thyroid hormone synthesis is completely reversed by an autocrine negative-feedback action of thyroglobulin (Tg) stored in the follicular lumen. In the present study, we investigated the potential effect of follicular Tg on SLC26A7 expression and found that follicular Tg significantly suppressed the promoter activity, mRNA level, and protein level of SLC26A7 in rat thyroid FRTL-5 cells. In addition, follicular Tg inhibited the ability of TSH to induce the membrane localization of SLC26A7. In rat thyroid sections, the expression of SLC26A7 was weaker in follicles with a higher concentration of Tg, as evidenced by immunofluorescence staining. These results indicate that Tg stored in the follicular lumen is a feedback suppressor of the expression and membrane localization of SLC26A7, thereby downregulating the transport of iodide into the follicular lumen.

Thyroid stimulating hormone suppresses the expression and activity of cytosolic sulfotransferase 1a1 in thyrocytes

Sulfonation is an important step in the metabolism of dopamine, estrogens, dehydroepiandrosterone, as well as thyroid hormones. However, the regulation of cytosolic sulfotransferases in the thyroid is not well understood. In a DNA microarray analysis of rat thyroid FRTL-5 cells, we found that the mRNA expression of 10 of 48 sulfotransferases was significantly altered by thyroid stimulating hormone (TSH), with that of sulfotransferase family 1A member 1 (SULT1A1) being the most significantly affected. Real-time PCR and Western blot analyses revealed that TSH, forskolin and dibutyryl cyclic AMP significantly suppressed SULT1A1 mRNA and protein levels in a time- and concentration-dependent manner. Moreover, immunofluorescence staining of FRTL-5 cells showed that SULT1A1 is localized in the perinuclear area in the absence of TSH but is spread throughout the cytoplasm with reduced fluorescence intensity in the presence of TSH. Sulfotransferase activity in FRTL-5 cells, measured using 3'-phosphoadenosine-5'-phosphosulfate as a donner and p-nitrophenol as an acceptor substrate, was significantly reduced by TSH. These findings suggest that the expression and activity of SULT1A1 are modulated by TSH in thyrocytes.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters (OPEs) are widespread in various environmental media, and can disrupt thyroid endocrine signaling pathways. Mechanisms by which OPEs disrupt thyroid hormone (TH) signal transduction are not fully understood. Here, we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways. OPEs can bind to transthyretin (TTR) and thyroxine-binding globulin, thereby affecting the transport of TH in the blood, and to the brain by TTR through the blood-brain barrier. When GH3 cells were exposed to OPEs, cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH. Cresyl diphenyl phosphate was shown to be an effective antagonist of TH. Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis. Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, signaling pathways related to thyroid endocrine functions, such as receptor-ligand binding and regulation of hormone levels, were identified as being affected by exposure to OPEs. Effects were also associated with the biosynthesis and metabolism of lipids, and neuroactive ligand-receptor interactions. These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

Intrathyroidal feedforward and feedback network regulating thyroid hormone synthesis and secretion

Thyroid hormones (THs), including T4 and T3, are produced and released by the thyroid gland under the stimulation of thyroid-stimulating hormone (TSH). The homeostasis of THs is regulated via the coordination of the hypothalamic-pituitary-thyroid axis, plasma binding proteins, and local metabolism in tissues. TH synthesis and secretion in the thyrocytes-containing thyroid follicles are exquisitely regulated by an elaborate molecular network comprising enzymes, transporters, signal transduction machineries, and transcription factors. In this article, we synthesized the relevant literature, organized and dissected the complex intrathyroidal regulatory network into structures amenable to functional interpretation and systems-level modeling. Multiple intertwined feedforward and feedback motifs were identified and described, centering around the transcriptional and posttranslational regulations involved in TH synthesis and secretion, including those underpinning the Wolff-Chaikoff and Plummer effects and thyroglobulin-mediated feedback regulation. A more thorough characterization of the intrathyroidal network from a systems biology perspective, including its topology, constituent network motifs, and nonlinear quantitative properties, can help us to better understand and predict the thyroidal dynamics in response to physiological signals, therapeutic interventions, and environmental disruptions.

Mutational and bioinformatics analysis of the NKX2.1 gene in a cohort of Iranian pediatric patients with congenital hypothyroidism (CH)

Congenital hypothyroidism (CH) occurs with a relatively alarming prevalence in infants, and if not diagnosed and treated in time, it can have devastating consequences for the development of the nervous system. CH is associated with genetic changes in several genes that encode transcription factors responsible for thyroid development, including mutations in the NK2 homeobox 1 (NKX2.1) gene, which encodes the thyroid transcription factor-1 (TTF-1). Although CH is frequently observed in pediatric populations, there is still a limited understanding of the genetic factors and molecular mechanisms contributing to this disease. The sequence of the NKX2.1 gene was investigated in 75 pediatric patients with CH by polymerase chain reaction (PCR), single-stranded conformation polymorphism (SSCP), and direct DNA sequencing. Four missense heterozygous variations were identified in exon 3 of the NKX2.1 gene, including three novel missense variations, namely c.708A>G, p.Gln202Arg; c.713T>G, p.Tyr204Asp; c.833T>G, p.Tyr244Asp, and a previously reported variant rs781133468 (c.772C>G, p.His223Gln). Importantly, these variations occur in highly conserved residues of the TTF-1 DNA-binding domain and were predicted by bioinformatics analysis to alter the protein structure, with a probable alteration in the protein function. These results indicate that nucleotide changes in the NKX2.1 gene may contribute to CH pathogenesis.

Mutational and bioinformatics analysis of the NKX2.1 gene in a cohort of Iranian pediatric patients with congenital hypothyroidism (CH)

Congenital hypothyroidism (CH) occurs with a relatively alarming prevalence in infants, and if not diagnosed and treated in time, it can have devastating consequences for the development of the nervous system. CH is associated with genetic changes in several genes that encode transcription factors responsible for thyroid development, including mutations in the NK2 homeobox 1 (NKX2.1) gene, which encodes the thyroid transcription factor-1 (TTF-1). Although CH is frequently observed in pediatric populations, there is still a limited understanding of the genetic factors and molecular mechanisms contributing to this disease. The sequence of the NKX2.1 gene was investigated in 75 pediatric patients with CH by polymerase chain reaction (PCR), single-stranded conformation polymorphism (SSCP), and direct DNA sequencing. Four missense heterozygous variations were identified in exon 3 of the NKX2.1 gene, including three novel missense variations, namely c.708A>G, p.Gln202Arg; c.713T>G, p.Tyr204Asp; c.833T>G, p.Tyr244Asp, and a previously reported variant rs781133468 (c.772C>G, p.His223Gln). Importantly, these variations occur in highly conserved residues of the TTF-1 DNA-binding domain and were predicted by bioinformatics analysis to alter the protein structure, with a probable alteration in the protein function. These results indicate that nucleotide changes in the NKX2.1 gene may contribute to CH pathogenesis.

Genome-Wide Association Analysis and Genomic Prediction of Thyroglobulin Plasma Levels

Thyroglobulin (Tg) is an iodoglycoprotein produced by thyroid follicular cells which acts as an essential substrate for thyroid hormone synthesis. To date, only one genome-wide association study (GWAS) of plasma Tg levels has been performed by our research group. Utilizing recent advancements in computation and modeling, we apply a Bayesian approach to the probabilistic inference of the genetic architecture of Tg. We fitted a Bayesian sparse linear mixed model (BSLMM) and a frequentist linear mixed model (LMM) of 7,289,083 variants in 1096 healthy European-ancestry participants of the Croatian Biobank. Meta-analysis with two independent cohorts (total n = 2109) identified 83 genome-wide significant single nucleotide polymorphisms (SNPs) within the ST6GAL1 gene (p<5×10-8). BSLMM revealed additional association signals on chromosomes 1, 8, 10, and 14. For ST6GAL1 and the newly uncovered genes, we provide physiological and pathophysiological explanations of how their expression could be associated with variations in plasma Tg levels. We found that the SNP-heritability of Tg is 17% and that 52% of this variation is due to a small number of 16 variants that have a major effect on Tg levels. Our results suggest that the genetic architecture of plasma Tg is not polygenic, but influenced by a few genes with major effects.

Molecular evidence reveals thyrotropin intervention enhances the risk of developing radioiodine-refractory differentiated thyroid carcinoma

Radioiodine (RAI) is the mainstay of treatment for differentiated thyroid carcinoma (DTC) following total thyroidectomy. Nevertheless, about 5% of patients with DTC are RAI-refractory (RAI-R). Understanding the molecular mechanisms associated with DTC during progression towards RAI-R DTC, including thyroid-stimulating hormone levels, may help to explain the pathophysiology of challenging RAI-R DTC clinical cases.

Regulation of solute carrier family 26 member 7 (Slc26a7) by thyroid stimulating hormone in thyrocytes

Iodine transportation is an important step in thyroid hormone biosynthesis. Uptake of iodine into the thyroid follicle is mediated mainly by the basolateral sodium-iodide symporter (NIS or solute carrier family 5 member 5: SLC5A5), and iodine efflux across the apical membrane into the follicular lumen is mediated by pendrin (SLC26A4). In addition to these transporters, SLC26A7, which has recently been identified as a causative gene for congenital hypothyroidism, was found to encode a novel apical iodine transporter in the thyroid. Although SLC5A5 and SLC26A4 have been well-characterized, little is known about SLC26A7, including its regulation by TSH, the central hormone regulator of thyroid function. Using rat thyroid FRTL-5 cells, we showed that the mRNA levels of Slc26a7 and Slc26a4, two apical iodine transporters responsible for iodine efflux, were suppressed by TSH, whereas the mRNA level of Slc5a5 was induced. Forskolin and dibutyryl cAMP (dbcAMP) had the same effect as that of TSH on the mRNA levels of these transporters. TSH, forskolin and dbcAMP also had suppressive effects on SLC26A7 promoter activity, as assessed by luciferase reporter gene assays, and protein levels, as determined by Western blot analysis. TSH, forskolin and dbcAMP also induced strong localization of Slc26a7 to the cell membrane according to immunofluorescence staining and confocal laser scanning microscopy. Together, these results suggest that TSH suppresses the expression level of Slc26a7 but induces its accumulation at the cell membrane, where it functions as an iodine transporter.

Thyrotropin regulation of differentiated gene transcription in adult human thyrocytes in primary culture

Thyroid transcription factors (TTFs) - NKX2-1, FOXE1, PAX8 and HHEX - regulate multiple genes involved in thyroid development in mice but little is known about TTF regulation of thyroid-specific genes - thyroglobulin (TG), thyroid peroxidase (TPO), deiodinase type 2 (DIO2), sodium/iodide symporter (NIS) and TSH receptor (TSHR) - in adult, human thyrocytes. Thyrotropin (thyroid-stimulating hormone, TSH) regulation of thyroid-specific gene expression in primary cultures of human thyrocytes is biphasic yielding an inverted U-shaped dose-response curve (IUDRC) with upregulation at low doses and decreases at high doses. Herein we show that NKX2-1, FOXE1 and PAX8 are required for TSH-induced upregulation of the mRNA levels of TG, TPO, DIO2, NIS, and TSHR whereas HHEX has little effect on the levels of these thyroid-specific gene mRNAs. We show that TSH-induced upregulation is mediated by changes in their transcription and not by changes in the degradation of their mRNAs. In contrast to the IUDRC of thyroid-specific genes, TSH effects on the levels of the mRNAs for NKX2-1, FOXE1 and PAX8 exhibit monophasic decreases at high doses of TSH whereas TSH regulation of HHEX mRNA levels exhibits an IUDRC that overlaps the IUDRC of thyroid-specific genes. In contrast to findings during mouse development, TTFs do not have major effects on the levels of other TTF mRNAs in adult, human thyrocytes. Thus, we found similarities and important differences in the regulation of thyroid-specific genes in mouse development and TSH regulation of these genes in adult, human thyrocytes.

Hyaluronan oligosaccharides modulate inflammatory response, NIS and thyreoglobulin expression in human thyrocytes

Autoimmune thyroid diseases, such as Hashimoto's thyroiditis, are characterized by lymphocytic infiltration and altered function of the thyroid. During inflammation, it has been reported a decreased expression in Tg and NIS, accompanied by an increase in HA production that accumulates in the gland. HA fragments produced in different pathological states can modulate gene expression in a variety of cell types and may prime inflammatory response by interacting with the TLR-2, TLR-4 and CD44 that, in turn, induce NF-kB activation finally responsible of inflammatory mediator transcription, such as IL-1β, TNF-α and IL-6. The aim of this study was to investigate the potential inflammatory effect and the biochemical pathways activated by 6-mer HA oligosaccharides in cultured human thyrocytes. 6-mer HA treatment induced up-regulation of TLR-2, TLR-4, CD44 mRNA and related protein levels, increased HA production and NF-kB activation, that in turn increased IL-1β and IL-6 concentrations. Instead, we found evidence of an opposite effect on thyroid specific-gene Tg and NIS, that were decreased after 6-mer HA addition. Thyrocytes exposition to specific blocking antibodies for TLR-2, TLR-4 and CD44 abolished up-regulation of NF-κB activation and the consequent pro-inflammatory cytokine production, while restored Tg and NIS levels. A further goal of this study was demonstrate that also other LMW HA have pro inflammatory proprieties. These data suggest that HA fragments, through the involvement of TLR-2, TLR-4 and CD44 signaling cascade, contribute to prime the inflammatory response in thyrocytes and, by reducing the expression of thyroid-specific genes, could promote the loss of function of gland such as in Hashimoto's thyroiditis.

Gut Microbiome and Radioiodine-Refractory Papillary Thyroid Carcinoma Pathophysiology

Gut microbiome (GM) might be associated with radioiodine (RAI)-refractory papillary thyroid carcinoma (PTC) through different mechanisms related to sodium/iodide (Na⁺/I^-) symporter (NIS) regulation. However, whether thyroid carcinoma (TC), especially RAI-refractory PTC, causes dysbiosis, or vice versa, is still unknown. Further studies are needed to investigate the mechanism between GM and RAI-refractory PTC.

Auto-Regulation of the Thyroid Gland Beyond Classical Pathways

This mini-review asks how self-regulation of the thyroid gland is realized at the cellular and molecular levels by canonical and non-canonical means. Canonical pathways of thyroid regulation comprise thyroid stimulating hormone-triggered receptor signaling. As part of non-canonical regulation, we hypothesized an interplay between protease-mediated thyroglobulin processing and thyroid hormone release into the circulation by means of thyroid hormone transporters like Mct8. We proposed a sensing mechanism by different thyroid hormone transporters, present in specific subcellular locations of thyroid epithelial cells, selectively monitoring individual steps of thyroglobulin processing, and thus, the cellular thyroid hormone status. Indeed, we found that proteases and thyroid hormone transporters are functionally inter-connected, however, in a counter-intuitive manner fostering self-thyrotoxicity in particular in Mct8- and/or Mct10-deficient mice. Furthermore, the possible role of the G protein-coupled receptor Taar1 is discussed, because we detected Taar1 at cilia of the apical plasma membrane of thyrocytes in vitro and in situ. Eventually, through pheno-typing Taar1-deficient mice, we identified a co-regulatory role of Taar1 and the thyroid stimulating hormone receptors. Recently, we showed that inhibition of thyroglobulin-processing enzymes results in disappearance of cilia from the apical pole of thyrocytes, while Taar1 is re-located to the endoplasmic reticulum. This pathway features a connection between thyrotropin-stimulated secretion of proteases into the thyroid follicle lumen and substrate-mediated self-assisted control of initially peri-cellular thyroglobulin processing, before its reinternalization by endocytosis, followed by extensive endo-lysosomal liberation of thyroid hormones, which are then released from thyroid follicles by means of thyroid hormone transporters.

A comparison of the thyroid disruption induced by decabrominated diphenyl ethers (BDE-209) and decabromodiphenyl ethane (DBDPE) in rats

In recent years, decabromodiphenyl ethane (DBDPE), a new alternative flame retardant to the decabrominated diphenyl ethers (BDE-209), is widely used in a variety of products. Previous studies have indicated that DBDPE, like BDE-209, could disrupt thyroid function. However, compared with BDE-209, the degrees of thyrotoxicosis induced by DBDPE were not clear. In addition, the mechanism of thyrotoxicosis induced by DBDPE or BDE-209 was still under further investigation. In this study, male rats as a model were orally exposed to DBDPE or BDE-209 by 5, 50, 500 mg/kg bw/day for 28 days. Then, we assessed the thyrotoxicosis of DBDPE versus BDE-209 and explored the mechanisms of DBDPE and BDE-209-induced thyrotoxicosis. Results showed that decreased free triiodothyronine (FT3) and increased thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) in serum were observed in both 500 mg/kg bw/day BDE-209 and DBDPE group. Decreased total thyroxine (TT4), total T3 (TT3), and free T4 (FT4) were only observed in BDE-209 group but not in DBDPE group. Histological examination and transmission electron microscope examination showed that high level exposure to BDE-209 and DBDPE both caused significant changes in histological structure and ultrastructure of the thyroid gland. Additionally, oxidative damages of thyroid gland (decreased SOD and GSH activities, and increased MDA content) were also observed in both BDE-209 and DBDPE groups. TG contents in the thyroid gland was reduced in BDE-209 group but not in DBDPE group. Both BDE-209 and DBDPE affected the expression of hypothalamic-pituitary-thyroid (HPT) axis related genes. These findings suggested that both BDE-209 and DBDPE exposure could disrupt thyroid function in the direction of hypothyroidism and the underlying mechanism was likely to be oxidative stress and perturbations of HPT axis. However, DBDPE was found to be less toxic than BDE-209.

Inhibitory effects of methimazole and propylthiouracil on iodotyrosine deiodinase 1 in thyrocytes

Methimazole (MMI) and propylthiouracil (PTU) are commonly used for the treatment of Graves' disease. They share similar inhibitory effects on thyroid hormone biosynthesis by interfering with thyroid peroxidase (TPO)-mediated oxidation and organification of iodine. However, their potential effects on other thyroid functional molecules have not been explored in depth. To identify novel effects of MMI and PTU, DNA microarray analysis, real-time PCR, Western blotting, immunofluorescence staining and confocal laser scanning microscopy were performed using FRTL-5 rat thyroid cells. DNA microarray analysis indicated that both MMI and PTU suppress iodotyrosine deiodinase 1 (Iyd, Dehal1) mRNA levels. Further studies revealed that Dehal1 mRNA levels was stimulated by TSH, insulin and serum, while it was suppressed by iodine and a follicular concentration of thyroglobulin. MMI and PTU significantly suppressed Dehal1 expression induced by TSH, insulin and serum. On the other hand, although MMI suppressed Dehal1 expression in the absence of TSH, PTU only weakly suppressed Dehal1 without TSH. These results suggest that PTU and MMI may use different mechanisms to regulate Dehal1 expression, and TSH may play essential and differential roles in mediating PTU and MMI signals in thyrocytes. The drugs also inhibited re-distribution of Dehal1 protein into newly formed lysosomes following thyroglobulin endocytosis. These findings imply complex and multifaceted regulation of Dehal1 in the thyroid and suggest that MMI and PTU modulate Dehal1 expression and distribution of the protein in thyrocytes to exert their effect.

Fluoride Exposure Induces Inhibition of Sodium/Iodide Symporter (NIS) Contributing to Impaired Iodine Absorption and Iodine Deficiency: Molecular Mechanisms of Inhibition and Implications for Public Health

The sodium iodide symporter (NIS) is the plasma membrane glycoprotein that mediates active iodide transport in the thyroid and other tissues, such as the salivary, gastric mucosa, rectal mucosa, bronchial mucosa, placenta and mammary glands. In the thyroid, NIS mediates the uptake and accumulation of iodine and its activity is crucial for the development of the central nervous system and disease prevention. Since the discovery of NIS in 1996, research has further shown that NIS functionality and iodine transport is dependent on the activity of the sodium potassium activated adenosine 5'-triphosphatase pump (Na+, K+-ATPase). In this article, I review the molecular mechanisms by which F inhibits NIS expression and functionality which in turn contributes to impaired iodide absorption, diminished iodide-concentrating ability and iodine deficiency disorders. I discuss how NIS expression and activity is inhibited by thyroglobulin (Tg), tumour necrosis factor alpha (TNF-α), transforming growth factor beta 1 (TGF-β1), interleukin 6 (IL-6) and Interleukin 1 beta (IL-1β), interferon-γ (IFN-γ), insulin like growth factor 1 (IGF-1) and phosphoinositide 3-kinase (PI3K) and how fluoride upregulates expression and activity of these biomarkers. I further describe the crucial role of prolactin and megalin in regulation of NIS expression and iodine homeostasis and the effect of fluoride in down regulating prolactin and megalin expression. Among many other issues, I discuss the potential conflict between public health policies such as water fluoridation and its contribution to iodine deficiency, neurodevelopmental and pathological disorders. Further studies are warranted to examine these associations.

Jinlida Granules Improve Dysfunction of Hypothalamic-Pituitary-Thyroid Axis in Diabetic Rats Induced by STZ

Objective

We aim to explore the effects and mechanisms of Jinlida granules on the dysfunction of hypothalamic-pituitary-thyroid (HPT) axis in diabetic rats induced by streptozotocin.

Methods

A total of 48 SD rats were randomized into normal control group (NC, n = 6) and diabetic group (n = 42). Rats in diabetic group were randomly divided into diabetes mellitus (DM) control group, low, medium, and high doses of Jinlida group (JL, JM, and JH), medium dose of Jinlida plus Tongxinluo group (JM + T), metformin group (Met), and Saxagliptin group (Sax) (n = 6 in each group). Diabetic rats were obtained by intraperitoneal injection of streptozotocin and sacrificed at 8 weeks to examine the function of HPT axis.

Results

Levels of fasting blood glucose (P < 0.05), pIκB, TNFα (P < 0.05), pNF-κB, and IL-6 (P < 0.01) in liver tissue and TSHR mRNA expression (P < 0.01) in diabetic group were significantly increased, while levels of serum T3 and T4, thyroid hormone receptor (TR) mRNA and Dio1 mRNA in liver tissue, and sodium iodide symporter (NIS) mRNA in thyroid tissue in diabetic group were significantly decreased compared with those in NC group (P < 0.01). Among diabetic groups, level of fasting blood glucose in JH, JM + T and Met group was lower (P < 0.05) compared with DM group. However, levels of serum T3 and T4, TR mRNA in liver tissue, TSHR, and NIS mRNA in thyroid tissue in JH, JM + T, Met, and Sax group were significantly increased (P < 0.01) compared to DM group. In contrast, levels of Dio1 mRNA, pI-κB in Met and JM + T groups, pNF-κB in JH, JM + T, and Met group, and TNFα and IL-6 in JM, JH, JM + T, and Met group were significantly decreased (P < 0.05). HE staining showed reduced thyroid follicular epithelium and follicular area, as well as increased colloid area in DM group, indicating impaired synthesis, reabsorption, and secretory of TH in diabetes, which was significantly improved in JH, JM + T, and Met groups.

Conclusion

HPT axis dysfunction in DM could be significantly improved by Jinlida granules. The mechanism might be associated with the anti-inflammatory effects involving NF-κB pathway. Our findings suggested the potential benefit of Jinlida granules for patients with HPT axis dysfunction and DM, which was to be verified by more experimental and clinical studies.

Specific alteration of gene expression profile in rats by treatment with thyroid toxicants that inhibit thyroid hormone synthesis

Transcriptomics technologies have been used for risk assessment of chemicals, mainly to predict the modes of action (MOAs) of chemicals or identify biomarkers. Transcriptomics data may also be helpful to understand MOAs of chemicals at the molecular level in more detail. As an example of the known MOAs, there are two MOAs of thyroid toxicity: inhibition of thyroid hormone synthesis ("direct" effect) and hypermetabolism of thyroid hormone by enzyme induction in liver ("indirect" effect). In the present study, global profiles of gene expression were analyzed in rats treated with chemicals acting directly on the thyroid (thyroid peroxidase inhibitors such as propylthiouracil and methimazole) and chemicals acting indirectly on the thyroid (hepatic enzyme inducers such as phenobarbital and pregnenolone-16α-carbonitrile) using microarrays. Using a subtraction method between these two types of chemicals, we identified characteristic gene expression changes on the thyroid hormone synthesis pathway by direct-acting chemicals. Based on the functions of these genes, alterations of their expression seem to indicate the results of thyroid peroxidase inhibition, and might be helpful in more accurate evaluation of MOAs for thyroid toxicity.

Thyroid hormone biosynthesis and release

Thyroid hormones (TH) 3,5,3',5'- tetraiodothyronine or thyroxine (T4) and 3,5,3'- triiodothyronine (T3) contain iodine atoms as part of their structure, and their synthesis occur in the unique structures called thyroid follicles. Iodide reaches thyroid cells through the bloodstream that supplies the basolateral plasma membrane of thyrocytes, where it is avidly taken up through the sodium/iodide symporter (NIS). Thyrocytes are also specialized in the secretion of the high molecular weight protein thyroglobulin (TG) in the follicular lumen. The iodination of the tyrosyl residues of TG preceeds TH biosynthesis, which depends on the interaction of iodide, TG, hydrogen peroxide (H₂O₂) and thyroid peroxidase (TPO) at the apical plasma membrane of thyrocytes. Thyroid hormone biosynthesis is under the tonic control of thyrotropin (TSH), while the iodide recycling ability is very important for normal thyroid function. We discuss herein the biochemical aspects of TH biosynthesis and release, highlighting the novel molecules involved in the process.

Histological and ultrastructural alterations of rat thyroid gland after short-term treatment with high doses of thyroid hormones

The aim of the present study was to investigate histological alterations of rat thyroid gland after short-term treatment with supraphysiological doses of thyroid hormones. Rats from experimental groups were treated with triiodothyronine (T3) or thyroxine (T4) during five days. In both treated groups, thyrocyte height was reduced and follicular lumens were distended. Progressive involutive changes of the thyroid parenchyma were apparent, including follicular remodeling (fusion) and death of thyrocytes. Morphological changes confirmed by quantitative analysis were more pronounced in the T4-treated group. Our results demonstrate that thyrotoxicosis, whether induced by T3 or T4, leads to different grades of thyroid tissue injury, including some irreversible damages. These changes might be explained at least in part by lack of trophic and cytoprotective effects of the thyroid stimulating hormone. Since the period required for morphophysiological recovery may be unpredictable, findings presented here should be taken into consideration in cases where the thyroid hormones are used as a treatment for thyroid and non-thyroid related conditions.

Follicular thyroglobulin induces cathepsin H expression and activity in thyrocytes

Thyroglobulin (Tg) stored in thyroid follicles exerts a potent negative-feedback effect on each step of pre-hormone biosynthesis, including Tg gene transcription and iodine uptake and organification, by suppressing the expression of specific transcription factors that regulate these steps. Pre-hormones are stored in the follicular colloid before being reabsorbed. Following lysosomal proteolysis of its precursor, thyroid hormone (TH) is released from thyroid follicles. Although the suppressive effects of follicular Tg on each step of pre-hormone biosynthesis have been extensively characterized, whether follicular Tg accumulation also affects hormone reabsorption, proteolysis, and secretion is unclear. In this study we explored whether follicular Tg can regulate the expression and function of the lysosomal endopeptidases cathepsins. We found that in the rat thyroid cell line FRTL-5 follicular Tg induced cathepsin H mRNA and protein expression, as well as cathepsin H enzyme activity. Double immunofluorescence staining showed that Tg endocytosis promoted cathepsin H translocalization into lysosomes where it co-localized with internalized Tg. These results suggest that cathepsin H is an active participant in lysosome-mediated pre-hormone degradation, and that follicular Tg stimulates mobilization of pre-hormones by activating cathepsin H-associated proteolysis pathways.

Effects of 2-iodohexadecanal in the physiology of thyroid cells

Iodide has direct effects on thyroid function. Several iodinated lipids are biosynthesized by the thyroid and they were postulated as intermediaries in the action of iodide. Among them, 2-iodohexadecanal (2-IHDA) has been identified and proposed to play a role in thyroid autoregulation. The aim of this study was to compare the effect of iodide and 2-IHDA on thyroid cell physiology. For this purpose, FRTL-5 thyroid cells were incubated with the two compounds during 24 or 48 h and several thyroid parameters were evaluated such as: iodide uptake, intracellular calcium and H₂O₂ levels. To further explore the molecular mechanism involved in 2-IHDA action, transcript and protein levels of genes involved in thyroid hormone biosynthesis, as well as the transcriptional expression of these genes were evaluated in the presence of iodide and 2-IHDA. The results obtained indicate that 2-IHDA reproduces the action of excess iodide on the "Wolff-Chaikoff" effect as well as on thyroid specific genes transcription supporting its role in thyroid autoregulation.

A Novel Role for Flotillin-Containing Lipid Rafts in Negative-Feedback Regulation of Thyroid-Specific Gene Expression by Thyroglobulin

BACKGROUND

Thyroglobulin (Tg) stored in thyroid follicles regulates follicular function in thyroid hormone (TH) synthesis by suppressing thyroid-specific gene expression in a concentration-dependent manner. Thus, Tg is an intrinsic negative-feedback regulator that can restrain the effect of thyrotropin (TSH) in the follicle. However, the underlying mechanisms by which Tg exerts its prominent autoregulatory effect following recognition by thyrocytes remains unclear.

METHODS

In order to identify potential proteins that recognize and interact with Tg, mass spectrometry was used to analyze immunoprecipitated Tg-bound proteins derived from Tg-treated rat thyroid FRTL-5 cells.

RESULTS

Flotillin 1 and flotillin 2, two homologs that are integral membrane proteins in lipid rafts, were identified as novel Tg-binding proteins with high confidence. Further studies revealed that flotillins physically interact with endocytosed Tg, and together these proteins redistribute from the cell membrane to cytoplasmic vesicles. Treatment with the lipid raft disrupter methyl-β-cyclodextrin abolished both the endocytosis and the negative-feedback effect of Tg on thyroid-specific gene expression. Meanwhile, siRNA-mediated knockdown of flotillin 1 or flotillin 2 also significantly inhibited Tg effects on gene expression.

CONCLUSION

Together these results indicate that flotillin-containing lipid rafts are essential for follicular Tg to be recognized by thyrocytes and exert its negative-feedback effects in the thyroid.

Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats

BACKGROUND

Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function.

METHODS

Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO₄ (0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later.

RESULTS

NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess.

CONCLUSIONS

The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.

Insights into the posttranslational structural heterogeneity of thyroglobulin and its role in the development, diagnosis, and management of benign and malignant thyroid diseases

Thyroglobulin (Tg) is the major glycoprotein produced by the thyroid gland, where it serves as a template for thyroid hormone synthesis and as an intraglandular store of iodine. Measurement of Tg levels in serum is of great practical importance in the follow-up of differentiated thyroid carcinoma (DTC), a setting in which elevated levels after total thyroidectomy are indicative of residual or recurrent disease. The most recent methods for serum Tg measurement are monoclonal antibody-based and are highly sensitive. However, major challenges remain regarding the interpretation of the results obtained with these immunometric methods, particularly in patients with endogenous antithyroglobulin antibodies or in the presence of heterophile antibodies, which may produce falsely low or high Tg values, respectively. The increased prevalence of antithyroglobulin antibodies in patients with DTC, as compared with the general population, raises the very pertinent possibility that tumor Tg may be more immunogenic. This inference makes sense, as the tumor microenvironment (tumor cells plus normal host cells) is characterized by several changes that could induce posttranslational modification of many proteins, including Tg. Attempts to understand the structure of Tg have been made for several decades, but findings have generally been incomplete due to technical hindrances to analysis of such a large protein (660 kDa). This review article will explore the complex structure of Tg and the potential role of its marked heterogeneity in our understanding of normal thyroid biology and neoplastic processes.

Short-term exposure of arsenite disrupted thyroid endocrine system and altered gene transcription in the HPT axis in zebrafish

Arsenic (As) pollution in aquatic environment may adversely impact fish health by disrupting their thyroid hormone homeostasis. In this study, we explored the effect of short-term exposure of arsenite (AsIII) on thyroid endocrine system in zebrafish. We measured As concentrations, As speciation, and thyroid hormone thyroxine levels in whole zebrafish, oxidative stress (H2O2) and damage (MDA) in the liver, and gene transcription in hypothalamic-pituitary-thyroid (HPT) axis in the brain and liver tissues of zebrafish after exposing to different AsIII concentrations for 48 h. Result indicated that exposure to AsIII increased inorganic As in zebrafish to 0.46-0.72 mg kg(-1), induced oxidative stress with H2O2 being increased by 1.4-2.5 times and caused oxidative damage with MDA being augmented by 1.6 times. AsIII exposure increased thyroxine levels by 1.3-1.4 times and modulated gene transcription in HPT axis. Our study showed AsIII caused oxidative damage, affected thyroid endocrine system and altered gene transcription in HPT axis in zebrafish.

The Emerging Roles of Thyroglobulin

Thyroglobulin (Tg), the most important and abundant protein in thyroid follicles, is well known for its essential role in thyroid hormone synthesis. In addition to its conventional role as the precursor of thyroid hormones, we have uncovered a novel function of Tg as an endogenous regulator of follicular function over the past decade. The newly discovered negative feedback effect of Tg on follicular function observed in the rat and human thyroid provides an alternative explanation for the observation of follicle heterogeneity. Given the essential role of the regulatory effects of Tg, we consider that dysregulation of normal Tg function is associated with multiple human thyroid diseases including autoimmune thyroid disease and thyroid cancer. Additionally, extrathyroid Tg may serve a regulatory function in other organs. Further exploration of Tg action, especially at the molecular level, is needed to obtain a better understanding of both the physiological and pathological roles of Tg.

Thyroglobulin suppresses thyroid-specific gene expression in cultures of normal but not neoplastic human thyroid follicular cells

CONTEXT

It was shown in the rat thyroid that thyroglobulin (Tg) stored in the follicular lumen is a potent regulator of thyroid-specific gene expression to maintain the function of individual follicles. However, the actions of Tg as a regulatory molecule in human thyroid have not been studied.

OBJECTIVE

Our objective was to determine the effect of Tg on gene expression in normal and diseased human thyroid and to examine whether the proposed model of negative-feedback autocrine regulation of thyroid function by Tg is applicable in the human as well as the rat.

DESIGN

Primary cultures of human thyrocytes were established from normal thyroid, Graves' disease thyroid, adenomatous goiter, follicular adenoma, and papillary carcinoma tissues obtained during surgery. Cells were stimulated with physiologic (ie, follicular) concentrations of Tg, and mRNA and protein expression of genes involved in thyroid hormonogenesis were evaluated. The effects of Tg on thyroid-specific gene expression were also assessed in 2 human papillary carcinoma cell lines.

RESULTS

Transcript levels of genes participating in thyroid hormone biosynthesis were significantly reduced by Tg in thyrocyte cultures derived from normal and Graves' thyroid, but not in cultures derived from thyroid neoplasms and adenomatous goiter.

CONCLUSION

It was confirmed that Tg acts as a negative-feedback regulator of gene expression in human thyrocytes, suggesting that Tg signaling may constitute a common mechanism for maintaining thyroid homeostasis in species with follicular thyroid morphology. However, certain diseases of intrinsic thyroid overgrowth appear to be associated with an escape from the regulatory mechanism of Tg.

Intrinsic regulation of thyroid function by thyroglobulin

BACKGROUND

The established paradigm for thyroglobulin (Tg) function is that of a high molecular weight precursor of the much smaller thyroid hormones, triiodothyronine (T3) and thyroxine (T4). However, speculation regarding the cause of the functional and morphologic heterogeneity of the follicles that make up the thyroid gland has given rise to the proposition that Tg is not only a precursor of thyroid hormones, but that it also functions as an important signal molecule in regulating thyroid hormone biosynthesis.

SUMMARY

Evidence supporting this alternative paradigm of Tg function, including the up- or downregulation by colloidal Tg of the transcription of Tg, iodide transporters, and enzymes employed in Tg iodination, and also the effects of Tg on the proliferation of thyroid and nonthyroid cells, is examined in the present review. Also discussed in detail are potential mechanisms of Tg signaling in follicular cells.

CONCLUSIONS

Finally, we propose a mechanism, based on experimental observations of Tg effects on thyroid cell behavior, that could account for the phenomenon of follicular heterogeneity as a highly regulated cycle of increasing and decreasing colloidal Tg concentration that functions to optimize thyroid hormone production through the transcriptional activation or suppression of specific genes.

Thyroglobulin increases thyroid cell proliferation via the suppression of specific microRNAs

Thyroglobulin (Tg), stored in the follicular lumen, has also been shown recently to perform two unexpected roles: as an autocrine negative-feedback suppressor of thyroid function in the presence of TSH and as a potent inducer of thyroid cell growth in the absence of TSH. However, the underlying molecular mechanism(s) remain unclear. To elucidate a molecular pathway linking Tg to increased cell proliferation, we examined the regulation of microRNAs (miRNAs) by Tg using an miRNA microarray. We identified 21 miRNAs whose expression was significantly suppressed by Tg in rat thyroid FRTL-5 cells. Using specific miRNA analogs, we determined that miR-16, miR-24, and miR-195 mediate the induction of thyroid cell growth by Tg. The expression of miR-16 and miR-195 target genes, Mapk8, Ccne1, and Cdc6, which were previously shown to be essential for TSH-stimulated thyroid cell growth, were also induced by Tg. Moreover, the Tg-induced expression of these genes was reduced by overexpression of miR-16 and miR-195. Similarly, the induction of c-Myc by Tg was reduced by miR-24 overexpression. These results suggest that Tg could alter thyroid cell proliferation by increasing the expression of cell division-related genes such as Mapk8, Ccne1, Cdc6, and c-Myc through its suppression of specific microRNAs (miR-16, miR-24, and miR-195). In addition, we identified phosphatidylinositol 3-kinase as a key signaling pathway, linking Tg with cell proliferation. The present data support an important role for miRNAs as effectors for the effect of Tg on cell proliferation and perhaps other functions of Tg in the thyroid cell.

Heterogeneous Immunoreactivity of Emerin, a Nuclear Envelope LEM-domain Protein, in Normal Thyroid Follicles

Emerin is a LEM domain-containing integral membrane protein of the vertebrate nuclear envelope. Recently it has been reported that emerin regulates tissue-specific gene/protein expression. We studied the relationship between emerin expression and follicle function in normal and hyperplastic human thyroid tissues using immunohistochemistry and statistical methods. Emerin immunoreactivity was heterogeneous among follicular cells and follicles in normal thyroid tissue. It tended to be strong in the nuclei of tall follicular cells of small follicles and weak or negative in the nuclei of flat follicular cells of large follicles. Follicles with strong expression of emerin were also strongly positive for thyroglobulin (Tg) and thyroxine (T4) in follicular cells and colloid substance, suggesting active functioning follicles. In contrast, large follicles with weak expression of emerin were also weak or negative for Tg and T4. Emerin immunoreactivity was strong in almost all nuclei of hyperplastic follicular cells in Graves' disease tissues. These findings suggest that emerin expression may be related with follicular function and may contribute to the understanding of hormonogenesis in normal thyroid follicles.

Oxidative damage to macromolecules in the thyroid - experimental evidence

Whereas oxidative reactions occur in all tissues and organs, the thyroid gland constitutes such an organ, in which oxidative processes are indispensable for thyroid hormone synthesis. It is estimated that huge amount of reactive oxygen species, especially of hydrogen peroxide (H₂O₂), are produced in the thyroid under physiological conditions, justifying the statement that the thyroid gland is an organ of “oxidative nature”. Apart from H₂O₂, also other free radicals or reactive species, formed from iodine or tyrosine residues, participate in thyroid hormone synthesis. Under physiological conditions, there is a balance between generation and detoxification of free radicals. Effective protective mechanisms, comprising antioxidative molecules and the process of compartmentalization of potentially toxic molecules, must have been developed in the thyroid to maintain this balance. However, with additional oxidative abuse caused by exogenous or endogenous prooxidants (ionizing radiation being the most spectacular), increased damage to macromolecules occurs, potentially leading to different thyroid diseases, cancer included.

Regulation of dual oxidase expression and H2O2 production by thyroglobulin

BACKGROUND

Thyroglobulin (Tg) is a macromolecular precursor in thyroid hormone synthesis to which iodine is stably bound. Tg, which is stored in the follicular space, is also a potent negative feedback regulator of follicular function, and this is achieved by suppressing mRNA levels of thyroid-specific genes such as the sodium/iodide symporter (Slc5a5), Tg, and thyroid peroxidase. Dual oxidase 1 (DUOX1) and DUOX2, originally identified in the thyroid, are nicotinamide adenine dinucleotide phosphate (NADPH) oxidases that are necessary to produce the H2O2 required for thyroid hormone biosynthesis. Since follicular Tg regulates the expression of genes that are essential for thyroid hormone synthesis, we hypothesized that Tg might also regulate DUOX expression and H2O2 production.

METHODS

Rat thyroid FRTL-5 cells were treated with Tg, and the mRNA expression of Duox1 and Duox2 and their corresponding maturation factors Duoxa1 and Duoxa2 were evaluated by DNA microarray and real-time PCR. Duox2 promoter activity was examined by luciferase reporter gene assay. Protein levels of DUOX2 were also examined by Western blot analysis. Intracellular H2O2 generation was quantified by a fluorescent dye, 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, and acetyl ester (CM-H2DCFDA).

RESULTS

mRNA levels of Duox2 and its activation factor Duoxa2 (but not Duox1 or Duoxa1) were significantly suppressed by Tg in a dose-dependent manner and a time-dependent fashion in rat thyroid FRTL-5 cells. DUOX2 promoter activity was significantly suppressed by Tg in a dose-dependent manner. Protein levels of DUOX2 and H2O2 generation in cells were also reduced by Tg treatment.

CONCLUSIONS

We show that physiological concentrations of Tg suppressed the expression and function of DUOX2 in thyroid cells. These results suggest that Tg is a strong suppressor of the expression and the activity of DUOX2/DUOXA2, thereby regulating iodide organification and hormone synthesis in the thyroid. The evidence supports a reported model in which accumulated Tg in thyroid follicles plays important roles in autoregulating the function of individual follicles, which produces the basis of follicular heterogeneity.

The effects of ammonium perchlorate on thyroid homeostasis and thyroid-specific gene expression in rat

Perchlorate, a kind of inorganic chemical, is mainly used in defense industry and widely used in other civilian areas. It was well known that perchlorate exerts its thyrotoxicant effect on thyroid homeostasis via competitive inhibition of iodide uptake. However, some details of mechanism by which perchlorate disturb thyroid homeostasis are unknown and remain to be elucidated. The present study aimed to investigate if iodide insufficiency in the thyroid is the main mechanism by which perchlorate exerts its effect on the thyroid gland. We highlighted and measured the gene expression of NIS, Tg, and TPO which involved in thyroid hormone biosynthesis. Thyroid effects of perchlorate were identified by assessing different responses of these genes at the treatments of perchlorate and iodine deficiency. The results indicated that high dose perchlorate (520 mg kg(-1) b.wt.) can induce a significant decrease in body weight and cause hypertrophy of thyroid gland, with a decreased level of FT3, FT4 and a remarkable increased level of TSH. In addition, the significant decreased gene expression of Thyroglobulin (Tg) and thyroperoxidase (TPO) were both observed at the treatment of high dose perchlorate. These results suggested that perchlorate can suppress gene expression of Tg and TPO which directly involved in biosynthesis of thyroid hormones, and may therefore aggravate the perturbation of thyroid homeostasis in addition to competitive inhibition of iodide uptake.

Propylthiouracil increases sodium/iodide symporter gene expression and iodide uptake in rat thyroid cells in the absence of TSH

BACKGROUND

Propylthiouracil (PTU) and methimazole (MMI) are drugs that are widely used to treat Graves' disease. Although both exert an antithyroid effect primarily by blocking thyroid peroxidase activity, their molecular structure and other actions are different. We hypothesized that PTU and MMI may have differential effects on thyroid-specific gene expression and function.

METHODS

The effects of PTU and MMI on thyroid-specific gene expression and function were examined in rat thyroid FRTL-5 cells using DNA microarray, reverse transcriptase (RT)-polymerase chain reaction (PCR), real-time PCR, Western blot, immunohistochemistry, and radioiodine uptake studies.

RESULTS

DNA microarray analysis showed a marked increase in sodium/iodide symporter (NIS) gene expression after PTU treatment, whereas MMI had no effect. RT-PCR and real-time PCR analysis revealed that PTU-induced NIS mRNA levels were comparable to those elicited by thyroid-stimulating hormone (TSH). PTU increased 5'-1880-bp and 5'-1052-bp activity of the rat NIS promoter. While PTU treatment also increased NIS protein levels, the size of the induced protein was smaller than that induced by TSH, and the protein localized predominantly in the cytoplasm rather than the plasma membrane. Accumulation of (125)I in FRTL-5 cells was increased by PTU stimulation, but this effect was weaker than that produced by TSH.

CONCLUSIONS

We found that PTU induces NIS expression and iodide uptake in rat thyroid FRTL-5 cells in the absence of TSH. Although PTU and MMI share similar antithyroid activity, their effects on other thyroid functions appear to be quite different, which could affect their therapeutic effectiveness.

Phylogenetic analysis of the human thyroglobulin regions

Thyroglobulin is a large protein present in all vertebrates. It is synthesized in the thyrocytes and exported to lumen of the thyroid follicle, where its tyrosine residues are iodinated . The iodinated thyroglobulin is reintegrated into the cell and processed (cleaved to free its two extremities) for thyroid hormone synthesis. Thyroglobulin sequence analysis has identified four regions of the molecule: Tg1, Tg2, Tg3 and ChEL. Structural abnormalities and mutations result in different pathological consequences, depending on the thyroglobulin region affected. We carried out a bioinformatic analysis of thyroglobulin, determining the origin and the function of each region. Our results suggest that the Tg1 region acts as a binding protein on the apical membrane, the Tg2 region is involved in protein adhesion and the Tg3 region is involved in determining the three-dimensional structure of the protein. The ChEL domain is involved in thyroglobulin transport, dimerization and adhesion. The presence of repetitive domains in the Tg1, Tg2 and Tg3 regions suggests that these domains may have arisen through duplication.

Thyroglobulin (Tg) activates MAPK pathway to induce thyroid cell growth in the absence of TSH, insulin and serum

The growth of thyroid cells is tightly regulated by thyroid stimulating hormone (TSH) through the cyclic adenosine 3', 5'-monophosphate (cAMP) signaling pathway by potentiating the mitogenic activity of insulin and insulin-like growth factors (IGFs). However, we recently reported that thyroglobulin (Tg), a major product of the thyroid, also induces the growth of thyroid cells cultured in 0.2% serum in the absence of TSH and insulin. In this report, we demonstrate that Tg induced phosphorylation of molecules of the c-Raf/MEK/ERK pathway of the mitogen-activated protein kinase (MAPK). The MEK-1/2 inhibitor PD98059 suppressed Tg-induced phosphorylation of ERK1/2 and reduced bromodeoxyuridine (BrdU) incorporation. Tg also induced expression of the essential transcriptional factors c-Myc, c-Fos and c-Jun and phosphorylation of the retinoblastoma (Rb) protein. The present results, together with the previous report, suggest that Tg utilizes multiple signaling cascades to induce thyroid cell growth independent of TSH/cAMP stimulation.

Identification of microRNAs that mediate thyroid cell growth induced by TSH

TSH is a major regulator of thyroid cell growth and endocrine function. It is known that cAMP and phosphatidylinositol 3-kinase (PI3K) are responsible for mediating the action of TSH. Activation of these signals results in the induction of a series of transcription factors and cell cycle regulating proteins, which induce cell proliferation. In addition to such canonical transcriptional regulation, it was recently shown that microRNA (miRNA or miR) constitutes another key mechanism for the regulation of gene expression. However, whether TSH action is mediated by miRNA in the thyroid is unknown. In this study, we have performed miRNA microarray analysis and demonstrated that TSH significantly decreases expression of 47 miRNA in thyroid cells. Among these, we have shown, using their specific agonists, that overexpression of miR-16 and miR-195 suppressed cell cycle progression and DNA synthesis that was induced by TSH. In silico analysis predicted that Mapk8, Ccne1, and Cdc6, the expression of which was up-regulated by TSH, are potential target genes for these miRNA, and overexpression of miR-16 and miR-195 suppressed expression of these target genes. The decrease of miR-16 and miR-195 expression by TSH was reproduced by forskolin and N(6),2'-O-dibutyryladenosine cAMP and reversed by the protein kinase A inhibitor H89 and the PI3K inhibitor LY294002. These results suggest that TSH activates cAMP/protein kinase A and PI3K cascades to decrease miR-16 and miR-195, which induce Mapk8, Ccne1, and Cdc6 to activate cell proliferation.

Upregulation of thyroid transcription factor-1 and human leukocyte antigen class I in Hashimoto's disease providing a clinical evidence for possible triggering autoimmune reaction

OBJECTIVE

An increase in the expression of autoantigens and their presenting molecules human leukocyte antigen (HLA) class I has been demonstrated to be responsible for autoimmune diseases. Thyroid transcription factor-1 (TTF-1 or NKX2-1) synchronously upregulates both HLA class I and thyroid-specific autoantigen, which may be involved in the pathological process of autoimmune thyroiditis. In this study, the expressions and potential role of TTF-1 and HLA class I in Hashimoto's disease (HT) were examined.

PATIENTS

In this study, 22 resection specimens clinically and histopathologically confirmed to have Hashimoto's disease and 30 normal thyroid specimens from adjacent tissues of thyroid adenoma were used.

MEASUREMENT

Western blot, real-time PCR, and immunohistochemistry were performed to assay TTF-1 and HLA class I in the thyrocytes of Hashimoto's disease as well as in the normal thyroid from adjacent tissues of thyroid adenoma.

RESULTS

The TTF-1 and HLA class I in Hashimoto's disease were significantly higher than those in the controls.

CONCLUSION

Upregulation of TTF-1 and HLA class I in Hashimoto's disease provide a clinical evidence for possible triggering of autoimmune reaction.

Clinical and molecular characteristics of Pendred syndrome

Pendred syndrome is an autosomal recessive disorder defined by sensorineural deafness, goiter and a partial defect in the organification of iodide. It is caused by biallelic mutations in the SLC26A4 gene, which encodes pendrin, a multifunctional anion exchanger. At the level of the inner ear, pendrin is important for the creation of a normal endolymph composition and the maintenance of the endocochlear potential. In the thyroid, pendrin is expressed at the apical membrane of thyroid follicular cells and it appears to be involved in mediating iodide efflux into the lumen and/or maintenance of the follicular pH. Goiter development and hypothyroidism vary among affected individuals and seem to be partially dependent on nutritional iodide intake. In the kidney, pendrin functions as a chloride/bicarbonate exchanger. Elucidation of the molecular basis of Pendred syndrome and the function of pendrin has provided unexpected novel insights into the pathophysiology of the inner ear, thyroid hormone synthesis, and chloride/bicarbonate exchange in the kidney.

Messenger RNA quantification after fluorescence-activated cell sorting using in situ hybridization

Recent studies using stem cells or cancer stem cells have revealed the importance of detecting minor populations of cells in blood or tissue and analyzing their biological characteristics. The only possible method for carrying out such procedures is fluorescence-activated cell sorting (FACS). However, FACS has the following two limitations. First, cells without an appropriate cell surface marker cannot be sorted. Second, some laborious procedures such as rapid sorting or treatment under sterilized conditions may require in order to analyze their biological characteristics. If a specific mRNA in a particular cell type can be stained with a florescent dye and then the cells can be sorted without causing RNA degradation, a more simple and universal method for sorting and analyzing cells with a specific gene expression pattern could be established since the biological characteristics of the sorted cells could then be determined by analyzing their gene expression profile. In this study, we established a basic protocol for messenger RNA quantification after FACS (FACS-mQ) using a cRNA probe. This method could be used for the detection and analysis of stem cells or cancer stem cells in various tissues.

The sodium iodide symporter (NIS) and potential regulators in normal, benign and malignant human breast tissue

Introduction

The presence, relevance and regulation of the Sodium Iodide Symporter (NIS) in human mammary tissue remains poorly understood. This study aimed to quantify relative expression of NIS and putative regulators in human breast tissue, with relationships observed further investigated in vitro.

Methods

Human breast tissue specimens (malignant n = 75, normal n = 15, fibroadenoma n = 10) were analysed by RQ-PCR targeting NIS, receptors for retinoic acid (RARα, RARβ), oestrogen (ERα), thyroid hormones (THRα, THRβ), and also phosphoinositide-3-kinase (PI3K). Breast cancer cells were treated with Retinoic acid (ATRA), Estradiol and Thyroxine individually and in combination followed by analysis of changes in NIS expression.

Results

The lowest levels of NIS were detected in normal tissue (Mean(SEM) 0.70(0.12) Log₁₀ Relative Quantity (RQ)) with significantly higher levels observed in fibroadenoma (1.69(0.21) Log₁₀RQ, p<0.005) and malignant breast tissue (1.18(0.07) Log₁₀RQ, p<0.05). Significant positive correlations were observed between human NIS and ERα (r = 0.22, p<0.05) and RARα (r = 0.29, p<0.005), with the strongest relationship observed between NIS and RARβ (r = 0.38, p<0.0001). An inverse relationship between NIS and PI3K expression was also observed (r = −0.21, p<0.05). In vitro, ATRA, Estradiol and Thyroxine individually stimulated significant increases in NIS expression (range 6–16 fold), while ATRA and Thyroxine combined caused the greatest increase (range 16–26 fold).

Conclusion

Although NIS expression is significantly higher in malignant compared to normal breast tissue, the highest level was detected in fibroadenoma. The data presented supports a role for retinoic acid and estradiol in mammary NIS regulation in vivo, and also highlights potential thyroidal regulation of mammary NIS mediated by thyroid hormones.