A Novel Transgenic Model to Study Thyroid Axis Activity in Early Life Stage Medaka

Identifying endocrine disrupting chemicals in order to limit their usage is a priority and required according to the European Regulation. There are no Organization for Economic Co-operation and Development (OECD) test guidelines based on fish available for the detection of Thyroid axis Active Chemicals (TACs). This study aimed to fill this gap by developing an assay at eleuthero-embryonic life stages in a novel medaka (Oryzias latipes) transgenic line. This transgenic line expresses green fluorescent protein (GFP) in thyrocytes, under the control of the medaka thyroglobulin gene promoter. The fluorescence expressed in the thyrocytes is inversely proportional to the thyroid axis activity. When exposed for 72 h to activators (triiodothyronine (T3) and thyroxine (T4)) or inhibitors (6-N-propylthiouracil (PTU), Tetrabromobisphenol A (TBBPA)) of the thyroid axis, the thyrocytes can change their size and express lower or higher levels of fluorescence, respectively. This reflects the regulation of thyroglobulin by the negative feedback loop of the Hypothalamic-Pituitary-Thyroid axis. T3, T4, PTU, and TBBPA induced fluorescence changes with the lowest observable effect concentrations (LOECs) of 5 μg/L, 1 μg/L, 8 mg/L, and 5 mg/L, respectively. This promising tool could be used as a rapid screening assay and also to help decipher the mechanisms by which TACs can disrupt the thyroid axis in medaka.

IL-10-TG/TPO-T4 axis, the target of bis (2-ethylhexyl) tetrabromophthalate on thyroid function imbalance

Bis (2-ethylhexyl) tetrabromophthalate (TBPH) is a new type of brominated flame retardant. Some studies suggest that TBPH exposure may be associated with thyroid damage. However, there is a paucity of research on the authentic exposure-related effects and molecular mechanisms in animals or cells. In this study, we used male Sprague-Dawley (SD) rats and the Nthy ori3-1 cell line (the human thyroid follicular epithelial cell) to explore the potential effects of TBPH (5, 50, 500 mg/kg and 1, 10, 100 nM) on the thyroid. The genes and their proteins of cytokines and thyroid-specific proteins, thyroglobulin (TG), thyroid peroxidase (TPO), and sodium iodide cotransporter (NIS) were examined to investigate the possible mechanisms. At the end of the experiment, it was found that 50 and 500 mg/kg TBPH could increase the levels of total thyroxine (TT4) and free thyroxine (FT4) significantly. The messenger RNAs (mRNAs) of Tg, Tpo, Interleukin-6 (Il6), and Interleukin-10 (Il10) in the thyroid tissues from the rats treated with 500 mg/kg were enhanced clearly. Meanwhile, the mRNAs of TG, TPO, IL6, and IL10 were elevated in Nthy ori3-1 cells treated with 100 nM TBPH as well. The mRNAs of TG and TPO were elevated after the knockdown of IL6. To our surprise, after the knockdown of IL10 or the treatment of anti-IL-10-receptor (anti-IL-10-R) antibody, the mRNAs of TG and TPO were significantly reduced, and the effects of TBPH were diminished. In conclusion, our results suggested that the IL-10-IL-10R-TG/TPO-T4 axis is one important target of TBPH in the thyroid.

Structural features of thyroglobulin linked to protein trafficking

Thyroglobulin must pass endoplasmic reticulum (ER) quality control to become secreted for thyroid hormone synthesis. Defective thyroglobulin, blocked in trafficking, can cause hypothyroidism. Thyroglobulin is a large protein (~2750 residues) spanning regions I-II-III plus a C-terminal cholinesterase-like domain. The cholinesterase-like domain functions as an intramolecular chaperone for regions I-II-III, but the folding pathway leading to successful thyroglobulin trafficking remains largely unknown. Here, informed by the recent three-dimensional structure of thyroglobulin as determined by cryo-electron microscopy, we have bioengineered three novel classes of mutants yielding three entirely distinct quality control phenotypes. Specifically, upon expressing recombinant thyroglobulin, we find that first, mutations eliminating a disulfide bond enclosing a 200-amino acid loop in region I have surprisingly little impact on the ability of thyroglobulin to fold to a secretion-competent state. Next, we have identified a mutation on the surface of the cholinesterase-like domain that has no discernible effect on regional folding yet affects contact between distinct regions and thereby triggers impairment in the trafficking of full-length thyroglobulin. Finally, we have probed a conserved disulfide in the cholinesterase-like domain that interferes dramatically with local folding, and this defect then impacts on global folding, blocking the entire thyroglobulin in the ER. These data highlight variants with distinct effects on ER quality control, inhibiting domain-specific folding; folding via regional contact; neither; or both.

The p.Pro2232Leu variant in the ChEL domain of thyroglobulin gene causes intracellular transport disorder and congenital hypothyroidism

Thyroglobulin (TG), the predominant glycoprotein of the thyroid gland, functions as matrix protein in thyroid hormonegenesis. TG deficiency results in thyroid dyshormonogenesis. These variants produce a heterogeneous spectrum of congenital goitre, with an autosomal recessive mode of inheritance. The purpose of this study was to identify and functionally characterize new variants in the TG gene in order to increase the understanding of the molecular mechanisms responsible for thyroid dyshormonogenesis. A total of four patients from two non-consanguineous families with marked alteration of TG synthesis were studied. The two families were previously analysed in our laboratory, only one deleterious allele, in each one, was detected after sequencing the TG gene (c.2359 C > T [p.Arg787*], c.5560 G > T [p.Glu1854*]). These findings were confirmed in the present studies by Next-Generation Sequencing. The single nucleotide coding variants of the TG gene were then analyzed to predict the possible variant causing the disease. The p.Pro2232Leu (c.6695 C > T), identified in both families, showing a low frequency population in gnomAD v2.1.1 database and protein homology, amino acid prediction, and 3D modeling analysis predict a potential pathogenic effect of this variant. We also transiently express p.Pro2232Leu in a full-length rat TG cDNA clone and confirmed that this point variant was sufficient to cause intracellular retention of mutant TG in HEK293T cells. Consequently, each family carried a compound heterozygous for p.Arg787*/p.Pro2232Leu or p.Glu1854*/p.Pro2232Leu variants. In conclusion, our results confirm the pathophysiological importance of altered TG folding as a consequence of missense variants located in the ChEL domain of TG.

Microcystin-LR induced transgenerational effects of thyroid disruption in zebrafish offspring by endoplasmic reticulum stress-mediated thyroglobulin accumulation and apoptosis

MC-LR can interfere with thyroid function in fish, but the underlying mechanism is still unclear. Current study focuses to study the intergenerational inheritance of MC-LR-induced thyroid toxicity in zebrafish and in rat thyroid cells. In vivo experiments, adult female zebrafish (F0) were exposed to MC-LR (0, 5, and 25 μg/L) for 90 days and mated with male zebrafish without MC-LR exposure to generate F1 generation. F1 embryos were allowed to develop normally to 7 days post-fertilization (dpf) in clear water. In the F0 generation, MC-LR induced disturbance of the hypothalamic-pituitary-thyroid (HPT) axis, leading to a decrease in the production of thyroid hormones. Maternal MC-LR exposure also induced growth inhibition by altering thyroid hormones (THs) homeostasis and interfering with thyroid metabolism and development in F1 offspring. Mechanistically, MC-LR caused excessive accumulation of ROS and induced ER stress that further lead to activation of UPR in the F0 and F1 offspring of zebrafish. Interestingly, our findings suggested that MC-LR exposure hampered thyroglobulin turnover by triggering IRE1 and PERK pathway in zebrafish and FRTL-5 thyroid cells, thus disturbing the thyroid endocrine system and contributing to the thyroid toxicity from maternal to its F1 offspring of zebrafish. Particularly, inhibition of the IRE1 pathway by siRNA could alleviate thyroid development injury induced by MC-LR in FRTL-5 cells. In addition, MC-LR induced thyroid cell apoptosis by triggering ER stress. Taken together, our results demonstrated that maternal MC-LR exposure causes thyroid endocrine disruption by ER stress contributing to transgenerational effects in zebrafish offspring.

Defective Thyroglobulin: Cell Biology of Disease

The primary functional units of the thyroid gland are follicles of various sizes comprised of a monolayer of epithelial cells (thyrocytes) surrounding an apical extracellular cavity known as the follicle lumen. In the normal thyroid gland, the follicle lumen is filled with secreted protein (referred to as colloid), comprised nearly exclusively of thyroglobulin with a half-life ranging from days to weeks. At the cellular boundary of the follicle lumen, secreted thyroglobulin becomes iodinated, resulting from the coordinated activities of enzymes localized to the thyrocyte apical plasma membrane. Thyroglobulin appearance in evolution is essentially synchronous with the appearance of the follicular architecture of the vertebrate thyroid gland. Thyroglobulin is the most highly expressed thyroid gene and represents the most abundantly expressed thyroid protein. Wildtype thyroglobulin protein is a large and complex glycoprotein that folds in the endoplasmic reticulum, leading to homodimerization and export via the classical secretory pathway to the follicle lumen. However, of the hundreds of human thyroglobulin genetic variants, most exhibit increased susceptibility to misfolding with defective export from the endoplasmic reticulum, triggering hypothyroidism as well as thyroidal endoplasmic reticulum stress. The human disease of hypothyroidism with defective thyroglobulin (either homozygous, or compound heterozygous) can be experimentally modeled in thyrocyte cell culture, or in whole animals, such as mice that are readily amenable to genetic manipulation. From a combination of approaches, it can be demonstrated that in the setting of thyroglobulin misfolding, thyrocytes under chronic continuous ER stress exhibit increased susceptibility to cell death, with interesting cell biological and pathophysiological consequences.

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.

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.

The structure of natively iodinated bovine thyroglobulin

Thyroglobulin is a homodimeric glycoprotein that is essential for the generation of thyroid hormones in vertebrates. Upon secretion into the lumen of follicles in the thyroid gland, tyrosine residues within the protein become iodinated to produce monoiodotyrosine (MIT) and diiodotyrosine (DIT). A subset of evolutionarily conserved pairs of DIT (and MIT) residues can then engage in oxidative coupling reactions that yield either thyroxine (T4; produced from coupling of a DIT `acceptor' with a DIT `donor') or triiodothyronine (T3; produced from coupling of a DIT acceptor with an MIT donor). Although multiple iodotyrosine residues have been identified as potential donors and acceptors, the specificity and structural context of the pairings (i.e. which donor is paired with which acceptor) have remained unclear. Here, single-particle cryogenic electron microscopy (cryoEM) was used to generate a high-resolution reconstruction of bovine thyroglobulin (2.3 Å resolution in the core region and 2.6 Å overall), allowing the structural characterization of two post-reaction acceptor-donor pairs as well as tyrosine residues modified as MIT and DIT. A substantial spatial separation between donor Tyr149 and acceptor Tyr24 was observed, suggesting that for thyroxine synthesis significant peptide motion is required for coupling at the evolutionarily conserved thyroglobulin amino-terminus.

Prostate-Specific Membrane Antigen Expression in Patients With Differentiated Thyroid Cancer With Thyroglobulin Elevation and Negative Iodine Scintigraphy Using 68Ga-PSMA-HBED-CC PET/CT

PURPOSE OF THE REPORT

Prostate-specific membrane antigen (PSMA) is a member of superfamily of zinc-dependent exopeptidases that is robustly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature including microvessels of thyroid tumors. Its expression in differentiated thyroid cancer (DTC) has been confirmed in many recent studies, but systematic studies exploring PSMA expression in patients with DTC with thyroglobulin elevation and negative iodine scintigraphy (TENIS) are lacking. The aim of the present study was to evaluate the role of PSMA scan in TENIS patients with DTC.

METHODS

Nine consecutive patients with DTC with proven TENIS syndrome (6 men and 3 women with age range 29-68 years and mean age of 48 years) underwent 18F-FDG PET/CT as per the institution protocol. Thereafter, they were subjected to 68Ga-PSMA-HBED-CC PET/CT as per the institution protocol within a week of FDG PET imaging. Prostate-specific membrane antigen expression (SUVmax) in the lesions was compared with 18F-FDG PET and CT scan findings.

RESULTS

In 5 of 9 patients with TENIS, the metastatic lesions showed PSMA expression. A total of 14 lesions were seen on the CT scan. Prostate-specific membrane antigen PET detected 9 of 14 lesions (64.28%) (SUVmax ranging from 10.1 to 45.67; median SUVmax of 16.31), whereas FDG PET was positive in 11 of 14 lesions (78.57%). The lesions that showed PSMA uptake was localized to bones (5 of 9) and lungs (4 of 9). Two lesions that were localized to iliac crest and acetabulum were missed on FDG PET but were seen on CT and PSMA PET scan.

CONCLUSIONS

The results of this pilot study indicate that 68Ga-HBED-CC-PSMA PET/CT demonstrates PSMA expression in TENIS patients with lesions being localized to the bones and lungs. 68Ga-PSMA PET/CT could be useful for the identification of TENIS patients who might benefit from PSMA-targeted radionuclide therapy.

Cryo-EM: A new dawn in thyroid biology

The thyroid gland accumulates the rare dietary element iodine and incorporates it into iodinated thyroid hormones, utilising several tightly regulated reactions and molecular mechanisms. Thyroid hormones are essential in vertebrates and play a central role in many biological processes, such as development, thermogenesis and growth. The control of these functions is exerted through the binding of hormones to nuclear thyroid hormone receptors that rule the transcription of numerous metabolic genes. Over the last 50 years, thyroid biology has been studied extensively at the cellular and organismal levels, revealing its multiple clinical implications, yet, a complete molecular understanding is still lacking. This includes the atomic structures of crucial pathway components that would be needed to elucidate molecular mechanisms. Here we review the currently known protein structures involved in thyroid hormone synthesis, regulation, transport, and actions. We also highlight targets for future investigations that will significantly benefit from recent advances in macromolecular structure determination by electron cryo-microscopy (cryo-EM). As an example, we demonstrate how cryo-EM was crucial to obtain the structure of the large thyroid hormone precursor protein, thyroglobulin. We discuss modern cryo-EM compared to other structure determination methods and how an integrated structural and cell biological approach will help filling the molecular knowledge gap in our understanding of thyroid hormone metabolism. Together with clinical, cellular and high-throughput 'omics' studies, atomic structures of thyroid components will provide an important framework to map disease mutations and to interpret and predict thyroid phenotypes.

Prediction of heparin binding of mutated short sequences of rat thyroglobulin

BACKGROUND

Binding of thyroglobulin (Tg) to heparin is involved in Tg transcytosis via megalin. Rat Tg (rTg) binds to heparin through an exposed carboxyl terminal region (RELPSRRLKRPLPVK, Arg2489-Lys2503) rich in positively charged residues. This region is not entirely conserved in human Tg (hTg) (Arg2489-Glu2503, REPPARALKRSLWVE), resulting in lower affinity binding. Here, we developed a score to predict to what extent secondary structure modifications affect the heparin-binding ability of rTg.

METHODS

We designed eight synthetic peptides, including one with the Arg2489-Lys2503 sequence of rTg (rTgP), one with the corresponding sequence of hTg (hTgP), and six "mutant" peptides, each carrying a point mutation obtained by replacing one amino acid residue of rTgP with the corresponding residue of hTgP. Heparin binding was assessed in solid-phase assays. The Bmax and the constants of dissociation (K_d) were calculated.

RESULTS

Using a no-fee online service, we obtained predictions of peptide secondary structures and developed a scoring system to estimate to what extent mutations are expected to modify rTg secondary structure. The score was designated as Probability of Secondary Structure Change (PSSC) and it significantly correlated with the BMax (R = 0.942, P < 0.001) and the K_ds (R = - 0.744, P < 0.01) of heparin binding of hTgP and of the "mutant" peptides.

CONCLUSIONS

The PSSC score allows predicting to what extent point mutations are likely to affect the heparin-binding ability of short sequences of proteins: in this case rTg, regardless of whether mutations affect charge of the sequence. The secondary structure of Tg is likely to play a role in heparin binding.

The Amino Acid Transporter Mct10/Tat1 Is Important to Maintain the TSH Receptor at Its Canonical Basolateral Localization and Assures Regular Turnover of Thyroid Follicle Cells in Male Mice

Cathepsin K-mediated thyroglobulin proteolysis contributes to thyroid hormone (TH) liberation, while TH transporters like Mct8 and Mct10 ensure TH release from thyroid follicles into the blood circulation. Thus, thyroid stimulating hormone (TSH) released upon TH demand binds to TSH receptors of thyrocytes, where it triggers Gαq-mediated short-term effects like cathepsin-mediated thyroglobulin utilization, and Gαs-mediated long-term signaling responses like thyroglobulin biosynthesis and thyrocyte proliferation. As reported recently, mice lacking Mct8 and Mct10 on a cathepsin K-deficient background exhibit excessive thyroglobulin proteolysis hinting towards altered TSH receptor signaling. Indeed, a combination of canonical basolateral and non-canonical vesicular TSH receptor localization was observed in Ctsk-/-/Mct8-/y/Mct10-/- mice, which implies prolonged Gαs-mediated signaling since endo-lysosomal down-regulation of the TSH receptor was not detected. Inspection of single knockout genotypes revealed that the TSH receptor localizes basolaterally in Ctsk-/- and Mct8-/y mice, whereas its localization is restricted to vesicles in Mct10-/- thyrocytes. The additional lack of cathepsin K reverses this effect, because Ctsk-/-/Mct10-/- mice display TSH receptors basolaterally, thereby indicating that cathepsin K and Mct10 contribute to TSH receptor homeostasis by maintaining its canonical localization in thyrocytes. Moreover, Mct10-/- mice displayed reduced numbers of dead thyrocytes, while their thyroid gland morphology was comparable to wild-type controls. In contrast, Mct8-/y, Mct8-/y/Mct10-/-, and Ctsk-/-/Mct8-/y/Mct10-/- mice showed enlarged thyroid follicles and increased cell death, indicating that Mct8 deficiency results in altered thyroid morphology. We conclude that vesicular TSH receptor localization does not result in different thyroid tissue architecture; however, Mct10 deficiency possibly modulates TSH receptor signaling for regulating thyrocyte survival.

Structure and genetic variants of thyroglobulin: Pathophysiological implications

Thyroglobulin (TG) plays a main role in the biosynthesis of thyroid hormones (TH), and, thus, it is involved in a wide range of vital functions throughout the life cycle of all vertebrates. Deficiency of TH production due to TG genetic variants causes congenital hypothyroidism (CH), with devastating consequences such as intellectual disability and impaired growth if untreated. To this day, 229 variations in the human TG gene have been identified while the 3D structure of TG has recently appeared. Although TG deficiency is thought to be of autosomal recessive inheritance, the introduction of massive sequencing platforms led to the identification of a variety of monoallelic TG variants (combined with mutations in other thyroid gene products) opening new questions regarding the possibility of oligogenic inheritance of the disease. In this review we discuss remarkable advances in the understanding of the TG architecture and the pathophysiology of CH associated with TG defects, providing new insights for the management of congenital disorders as well as counseling benefits for families with a history of TG abnormalities. Moreover, we summarize relevant aspects of TH synthesis within TG and offer an updated analysis of animal and cellular models of TG deficiency for pathophysiological studies of thyroid dyshormonogenesis while highlighting perspectives for new investigations. All in all, even though there has been sustained progress in understanding the role of TG in thyroid pathophysiology during the past 50 years, functional characterization of TG variants remains an important area of study for future advancement in the field.

68Ga-FAPI PET/CT in Thyroid Cancer With Thyroglobulin Elevation and Negative Iodine Scintigraphy

ABSTRACT

Differentiated thyroid cancer with thyroglobulin elevation and negative iodine scintigraphy (TENIS) syndrome is a diagnostic and therapy dilemma. In this study, we present a case of TENIS with detectable metastases in the larynx and lung on the CT scan. 68Ga-fibroblast activation protein inhibitor (FAPI) PET/CT was performed for further detection of tumor recurrence and metastases, which showed intense 68Ga-FAPI activity in the metastatic lesions. To the best of our knowledge, this is the first case of TENIS presenting with FAPI-avid metastatic lesions, demonstrating its usefulness for localizing recurrent or metastatic lesions in patients with TENIS.

Possible mechanism of bamboo shoots (Bambusa balcooa) induced thyroid disruption - An in vitro study

Endemic goitre and associated iodine deficiency disorders (IDDs) are a major concern in public health even in the period of post salt iodization in many regions. Among others the consumption of cyanogenic plants found responsible for the persistence of such diseases. Bamboo shoots (BS) is one such cyanogenic plant food that caused disruption of certain thyroid hormone synthesizing regulatory element as has already been reported in our earlier study. In this investigation the possible mechanism of thyrocytes disruption along with interruption of thyroid hormone biosynthesis by BS has been worked out. Commonly consumed BS, Bambusa Balcooa Roxb (BBR) water extract was analysed by GC MS; three doses below IC50 were administered to thyrocytes in culture with and without iodine. Expressions of thyroglobulin (Tg), pendrin (PDS) and monocarboxylate transporter 8 (MCT8) were evaluated in thyrocytes with cell cycle analysis, reactive oxygen species (ROS) generation, DNA oxidation and apoptotic regulation through Bax, Bcl-2 and p53. Phytochemical analysis of BBR extract revealed the presence of precursors and metabolic end products of cyanogenic glycosides. Dose dependent decrease in expression of Tg and PDS with concomitant decrease in gene expression of these with MCT8 were observed. Increased ROS, DNA oxidation and associated imbalance were found through increased Bax and p53 with decreased Bcl-2 that perturbed thyrocytes cell cycle. Cyanogenic constituents of BBR generates ROS associated oxidative changes in thyrocytes with DNA damage and oxidation and cell cycle disruption followed by inhibition of thyroid hormone synthesizing regulatory elements; addition of extra iodine showed partial prevention.

The Thyroid Hormone Transporter Mct8 Restricts Cathepsin-Mediated Thyroglobulin Processing in Male Mice through Thyroid Auto-Regulatory Mechanisms That Encompass Autophagy

The thyroid gland is both a thyroid hormone (TH) generating as well as a TH responsive organ. It is hence crucial that cathepsin-mediated proteolytic cleavage of the precursor thyroglobulin is regulated and integrated with the subsequent export of TH into the blood circulation, which is enabled by TH transporters such as monocarboxylate transporters Mct8 and Mct10. Previously, we showed that cathepsin K-deficient mice exhibit the phenomenon of functional compensation through cathepsin L upregulation, which is independent of the canonical hypothalamus-pituitary-thyroid axis, thus, due to auto-regulation. Since these animals also feature enhanced Mct8 expression, we aimed to understand if TH transporters are part of the thyroid auto-regulatory mechanisms. Therefore, we analyzed phenotypic differences in thyroid function arising from combined cathepsin K and TH transporter deficiencies, i.e., in Ctsk^-/-/Mct10^-/-, Ctsk^-/-/Mct8^-/y, and Ctsk^-/-/Mct8^-/y/Mct10^-/-. Despite the impaired TH export, thyroglobulin degradation was enhanced in the mice lacking Mct8, particularly in the triple-deficient genotype, due to increased cathepsin amounts and enhanced cysteine peptidase activities, leading to ongoing thyroglobulin proteolysis for TH liberation, eventually causing self-thyrotoxic thyroid states. The increased cathepsin amounts were a consequence of autophagy-mediated lysosomal biogenesis that is possibly triggered due to the stress accompanying intrathyroidal TH accumulation, in particular in the Ctsk^-/-/Mct8^-/y/Mct10^-/- animals. Collectively, our data points to the notion that the absence of cathepsin K and Mct8 leads to excessive thyroglobulin degradation and TH liberation in a non-classical pathway of thyroid auto-regulation.

Primary Cilia Mediate TSH-Regulated Thyroglobulin Endocytic Pathways

Primary cilia are sensory organelles with a variety of receptors and channels on their membranes. Recently, primary cilia were proposed to be crucial sites for exocytosis and endocytosis of vesicles associated with endocytic control of various ciliary signaling pathways. Thyroglobulin (Tg) synthesis and Tg exocytosis/endocytosis are critical for the functions of thyroid follicular cells, where primary cilia are relatively well preserved. LRP2/megalin has been detected on the apical surface of absorptive epithelial cells, including thyrocytes. LRP2/megalin on thyrocytes serves as a Tg receptor and can mediate Tg endocytosis. In this study, we investigated the role of primary cilia in LRP2/megalin expression in thyroid gland stimulated with endogenous TSH using MMI-treated and Tg-Cre;Ift88^flox/flox mice. LRP2/megalin expression in thyroid follicles was higher in MMI-treated mice than in untreated control mice. MMI-treated mice exhibited a significant increase in ciliogenesis in thyroid follicular cells relative to untreated controls. Furthermore, MMI-induced ciliogenesis accompanied increases in LRP2/megalin expression in thyroid follicular cells, in which LRP2/megalin was localized to the primary cilium. By contrast, in Tg-Cre;Ift88^flox/flox mice, thyroid with defective primary cilia expressed markedly lower levels of LRP2/megalin. Serum Tg levels were elevated in MMI-treated mice and reduced in Tg-Cre;Ift88^flox/flox mice. Taken together, these results indicate that defective ciliogenesis in murine thyroid follicular cells is associated with impaired LRP2/megalin expression and reduced serum Tg levels. Our results strongly suggest that primary cilia harbors LRP2/megalin, and are involved in TSH-mediated endocytosis of Tg in murine thyroid follicles.

Mice Hypomorphic for Keap1, a Negative Regulator of the Nrf2 Antioxidant Response, Show Age-Dependent Diffuse Goiter with Elevated Thyrotropin Levels

Background: Familial nontoxic multinodular goiter (MNG) is a rare disease. One of the associated genes is Kelch-like ECH-associated protein 1 (KEAP1), which encodes the main inhibitor of nuclear factor erythroid 2-related transcription factor 2 (Nrf2), a central mediator of antioxidant responses. The association of KEAP1 with familial MNG is based on only two loss-of-function mutations identified in two families, only one of which included proper phenotyping and adequate demonstration of co-segregation of the phenotype and the mutation. There is no experimental evidence from model organisms to support that decreased Keap1 levels can, indeed, cause goiter. This study used mice hypomorphic for Keap1 to test whether decreased Keap1 expression can cause goiter, and to characterize the activation status of Nrf2 in their thyroid. Methods: C57BL/6J Keap1flox/flox (Keap1 knock-down [Keap1KD]) mice were studied at 3 and 12 months of age. Plasma and thyroid glands were harvested for evaluation of thyroid function tests and for gene and protein expression by real-time polymerase chain reaction and immunoblotting, respectively. Results: Keap1KD mice showed diffuse goiter that began to develop in early adult life and became highly prominent and penetrant with age. The goiter was characterized by a markedly increased size of thyroid follicles, most notably of the colloid compartment, and by absence of thyroid nodules or hyperplasia. Keap1KD mice also showed decreased T4 levels in early adult life that were eventually well compensated over time by increased thyrotropin (TSH) levels. Nrf2 was activated in the thyroid of Keap1KD mice. Despite a known stimulatory effect of Nrf2 on thyroglobulin (Tg) gene transcription and Tg protein abundance, the expression levels were decreased in the thyroid of Keap1KD mice. No clear patterns were observed in the expression profiles of other thyroid hormone synthesis-specific factors, with the exception of Tg-processing and Tg-degrading cathepsins, including an increase in mature forms of cathepsins D, L, and S. Conclusions: Keap1KD mice develop age-dependent diffuse goiter with elevated TSH levels. The precise mechanism accounting for the thyroidal phenotype remains to be elucidated, but it may involve enhanced Tg solubilization and excessive lysosomal Tg degradation.

Thyroglobulin Interactome Profiling Defines Altered Proteostasis Topology Associated With Thyroid Dyshormonogenesis

Thyroglobulin (Tg) is a secreted iodoglycoprotein serving as the precursor for triiodothyronine and thyroxine hormones. Many characterized Tg gene mutations produce secretion-defective variants resulting in congenital hypothyroidism. Tg processing and secretion is controlled by extensive interactions with chaperone, trafficking, and degradation factors comprising the secretory proteostasis network. While dependencies on individual proteostasis network components are known, the integration of proteostasis pathways mediating Tg protein quality control and the molecular basis of mutant Tg misprocessing remain poorly understood. We employ a multiplexed quantitative affinity purification-mass spectrometry approach to define the Tg proteostasis interactome and changes between WT and several congenital hypothyroidism variants. Mutant Tg processing is associated with common imbalances in proteostasis engagement including increased chaperoning, oxidative folding, and engagement by targeting factors for endoplasmic reticulum-associated degradation. Furthermore, we reveal mutation-specific changes in engagement with N-glycosylation components, suggesting distinct requirements for 1 Tg variant on dual engagement of both oligosaccharyltransferase complex isoforms for degradation. Modulating dysregulated proteostasis components and pathways may serve as a therapeutic strategy to restore Tg secretion and thyroid hormone biosynthesis.

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.

False-positive staining of thyroglobulin distinguished from mixed medullary and follicular thyroid carcinoma by duplex in situ hybridization

Medullary thyroid carcinoma (MTC) may mimic mixed medullary and follicular thyroid carcinoma (MMFTC). MTC originates from para-follicular cells, while MMFTC is an uncommon tumor characterized by coexistence of follicular and para-follicular cell-derived tumor populations. A 35-year-old woman was diagnosed with MTC but showed a hot nodule in thyroid scintigraphy. The tumor included diffusely-spread follicular lesions within it, which were immunostained with thyroglobulin and calcitonin. Immunofluorescence showed the presence of several tumor cells that were double-stained with thyroglobulin and calcitonin. To clarify whether or not the tumor was MMFTC, we used duplex in situ hybridization (ISH). Thyroglobulin and calcitonin-related polypeptide alpha mRNA were not expressed together in a single cell, so we suspected false-positive staining of tumor cells with thyroglobulin. To make comparisons with other follicular lesions in MTC, we searched our hospital database. Five cases within a ten-year period had been pathologically diagnosed as MTC. All had follicular lesions in the tumor, but unlike the other case, they were peripherally localized. Dual differentiation into follicular or para-follicular tumor cells was not indicated by either immunofluorescence or duplex ISH. Compared with the case suspected to be MMFTC, there was only mild invasion of tumor cells into the follicular epithelium. The extent of follicular lesions and invasiveness of tumor cells may be associated with pseudo-staining of thyroglobulin in MTC. Duplex ISH can distinguish MTC that are stained with thyroglobulin from MMFTC.

A Novel Mouse Model of Autoimmune Thyroiditis Induced by Immunization with Adenovirus Containing Full-Length Thyroglobulin cDNA: Implications to Genetic Studies of Thyroid Autoimmunity

Background: Thyroglobulin (TG) is a key autoantigen in autoimmune thyroid diseases (AITD). Several single nucleotide polymorphisms (SNPs) in the TG locus were shown to be strongly associated with disease susceptibility in both humans and mice, and autoimmune response to TG is the earliest event in the development of thyroid autoimmunity in mice. The classical model of experimental autoimmune thyroiditis (EAT) is induced by immunizing mice with TG protein together with an adjuvant to break down immune tolerance. The classical EAT model has limited utility in genetic studies of TG since it does not allow testing the effects of TG sequence variants on the development of autoimmune thyroiditis. In this study, we have immunized CBA-J mice, an EAT-susceptible strain, with an adenovirus vector encoding the full-length human TG (hTG) to generate a model of EAT in which the TG sequence can be manipulated to test AITD-associated TG SNPs. Methods: We immunized CBA-J mice with hTG-expressing adenovirus following the well-recognized experimental autoimmune Graves' disease protocol that also uses an adenovirus vector to deliver the immunogen. Results: After hTG adenovirus immunizations, mice developed higher T cell proliferative and cytokine responses to hTG and TG2098 (a major T cell epitope in AITD) and higher titers of TG and thyroperoxidase autoantibodies compared with mice immunized with control LacZ-expressing adenovirus. The mice, however, did not develop thyroidal lymphocytic infiltration and hypothyroidism. Conclusions: Our data describe a novel murine model of autoimmune thyroiditis that does not require the use of adjuvants to break down tolerance and that will allow investigators to test the effects of hTG variants in the pathoetiology of Hashimoto's thyroiditis.

Perinatal low-dose PBDE-47 exposure hampered thyroglobulin turnover and induced thyroid cell apoptosis by triggering ER stress and lysosomal destabilization contributing to thyroid toxicity in adult female rats

Evidence demonstrates that 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) is able to disturb thyroid hormones (THs) homeostasis, yet the mechanisms remain unknown. We sought to investigate the effects of PBDE-47 on endoplasmic reticulum (ER) and lysosomes in thyroids. Using female Sprague-Dawley rats orally administered PBDE-47 at environmentally relevant doses (0.1, 1.0, 10 mg/kg/day) beginning ten days before breeding and ending at weaning, we showed that perinatal PBDE-47 exposure resulted in a reduction in serum THs levels and relative thyroid weight in adult female rats. These were accompanied by thyroid structural abnormalities with cell apoptosis. Mechanistically, PBDE-47 caused ER stress and activation of unfolded protein response (UPR). Moreover, PBDE-47 elicited lysosomal membrane permeabilization and the release of cathepsin. Importantly, the apoptotic cells co-localized with IRE1α, a stress sensor protein of UPR branch that mediates ER stress-induced apoptosis, or cathepsin B, a lysosomal cysteine protease that is involved in thyroglobulin, the precursor of THs, degradation and apoptosis induction. Interestingly, thyroglobulin was accumulated and predominantly presented in cells harboring compromised ER or lysosomal activity. Collectively, our findings suggest that perinatal low-dose PBDE-47 exposure hampers thyroglobulin turnover and induces thyroid cell apoptosis by triggering ER stress and lysosomal destabilization contributing to thyroid toxicity in adult female rats.

Ex vivo model for elucidating the functional and structural differentiation of the embryonic mouse thyroid

Terminal thyroid gland differentiation - the last developmental step needed to enable thyroid hormone (T4) synthesis - involves profound structural and biochemical changes in the thyroid follicular cells (TFCs). We aimed to develop an ex vivo thyroid model of embryonic mouse thyroid that would replicate the in vivo TFC differentiation program. E13.5 thyroid explants were cultured ex vivo in chemically defined medium for 7 days. Immunostaining and qPCR of thyroid explants showed thyroglobulin production onset, follicle formation, and T4 synthesis onset in 1-, 3-, and 5-day-old cultures, respectively. Differentiation was maintained and follicular growth continued throughout the 7-day culture period. Pharmacological approaches to culture inhibition were performed successfully in the ex vivo thyroids. Our robust and well described ex vivo thyroid culture model replicates the sequence of thyroid differentiation to T4 synthesis seen in vivo. This model can be used to test the effects of pharmacological inhibitors on thyroid hormone production.

Histopathological and Immunohistochemical Characteristics of Thyroid Carcinoma in the Dog

Thyroid carcinomas are a common form of endocrine neoplasia in dogs. In the present study, we combined histopathology with immunohistochemistry (IHC) to search for the presence of oestrogen receptor alpha (ORα), Cox-2 and Ki67 in canine thyroid carcinomas. Forty-eight thyroid carcinomas were diagnosed throughout the study period. Thyroglobulin and calcitonin IHC distinguished between thyroid tumours with a follicular and medullary (C-cell) origin, respectively. IHC-based diagnosis showed that 42 (87.50%) of the cases were follicular cell carcinoma. In these cases, the follicular-compact pattern was the most frequent (n = 20/42; 47.62%) and six cases (12.5%) were medullary cell (C-cell) carcinomas. Both medullary (C-cell) and follicular carcinomas expressed Ki67 and Cox-2. No differences were observed between medullary and follicular carcinomas with respect to expression of Ki67 (P = 0.34) and Cox-2 (P = 0.9523) markers. A total of 4.17% (n = 2/48) of thyroid carcinomas showed positive nuclear labelling for ORα, suggesting that oestrogen does not directly participate in the pathogenesis of canine thyroid neoplasia.

New Thieno-[2,3-d]pyrimidine-Based Functional Antagonist for the Receptor of Thyroid Stimulating Hormone

Thyroid stimulating hormone (TSH) receptor antagonists are required for the treatment of TSH-dependent tumors and Graves disease. We developed the compound 5-amino-N-(tert-butyl)-4-(4-iodophenyl)-2-(methylthio)thieno[2,3-d]pyrimidine-6-carboxamide (TP48) and showed that it reduces the TSH-stimulated adenylate cyclase activity in rat thyroid membranes. Pretreatment of rats with compound TP48 (ip, 40 mg/kg) reduced the increase in the levels of total and free thyroxin in blood and the increase in the expression of thyroglobulin and D2 deiodinase genes in the thyroid gland, which are responsible for the synthesis of thyroid hormones, which were caused by intranasal administration of thyroliberin to animals (300 μg/kg). These data indicate that compound TP48 is a functional antagonist of the TSH receptor and can be used to correct the thyroid status in hyperthyroidism.

Development of an In Vitro Human Thyroid Microtissue Model for Chemical Screening

Thyroid hormones (TH) are essential for regulating a number of diverse physiological processes required for normal growth, development, and metabolism. The US EPA Endocrine Disruptor Screening Program (EDSP) has identified several molecular thyroid targets relevant to hormone synthesis dynamics that have been adapted to high-throughput screening (HTS) assays to rapidly evaluate the ToxCast/Tox21 chemical inventories for potential thyroid disrupting chemicals (TDCs). The uncertainty surrounding the specificity of active chemicals identified in these screens and the relevance to phenotypic effects on in vivo human TH synthesis are notable data gaps for hazard identification of TDCs. The objective of this study was to develop a medium-throughput organotypic screening assay comprised of reconstructed human thyroid microtissues to quantitatively evaluate the disruptive effects of chemicals on TH production and secretion. Primary human thyroid cells procured from qualified euthyroid donors were analyzed for retention of NK2 homeobox 1 (NKX2-1), Keratin 7 (KRT7), and Thyroglobulin (TG) protein expression by high-content image analysis to verify enrichment of follicular epithelial cells. A direct comparison of 2-dimensional (2D) and 3-dimensional (3D) 96-well culture formats was employed to characterize the morphology, differential gene expression, TG production, and TH synthesis over the course of 20 days. The results indicate that modeling human thyroid cells in the 3D format was sufficient to restore TH synthesis not observed in the 2D culture format. Inhibition of TH synthesis in an optimized 3D culture format was demonstrated with reference chemicals for key molecular targets within the thyroid gland. Implementation of the assay may prove useful for interpreting phenotypic effects of candidate TDCs identified by HTS efforts currently underway in the EDSP.

Morphological and functional changes in neonatally X-irradiated thyroid gland in rats

Exposure to ionized radiation in childhood has been recognized as a risk factor for the development of thyroid cancer and possibly for other thyroid disorders. However, the effects of neonatal radiation exposure on thyroid morphology and functions have never been explored despite its potential importance. One-week-old male Wistar rats were subjected to cervical X-irradiation at 6 and 12 Gy. Animals were examined at the ages of 2, 8 and 18 weeks old. For comparison, 8-week-old rats were cervically X-irradiated at the same doses. Thyroid histology was examined by computer-assisted microscopy to measure areas of colloid and epithelium of thyroid follicles as well as epithelial heights. In rats that received cervical X-irradiation at 1 week old, the colloid size of thyroid follicles decreased at the age of 8 weeks old in a radiation-dose dependent manner. This morphological change was persistently found at 18 weeks old. There were no significant differences in serum total T3 or T4 levels among the groups. Serum TSH levels increased significantly in 8-week-old rats neonatally X-irradiated. Thyroglobulin (Tg) mRNA and protein expressions were significantly decreased in the neonatally-irradiated group while thyroid peroxidase mRNA express increased at 18 weeks old. None of these changes were observed in the rats X-irradiated at 8 weeks old. In conclusion, our results clearly demonstrated that neonatal rat thyroid was sensitive to ionized radiation, developing specific morphological changes characterized by smaller thyroid follicles along with changes in serum TSH levels and Tg expressions in the thyroid tissue.

Diagnostic values of thyroglobulin in lymph node fine-needle aspiration washout: a systematic review and meta-analysis diagnostic values of FNA-Tg

Thyroglobulin measurement in the needle washout after fine-needle aspiration (FNA-Tg) served as an important measurement for suspicious recurrent or metastatic lesions. We conducted a pooled analysis to evaluate the diagnostic accuracy of FNA-Tg and searched electronic databases for original articles in English from 1993 through 2017. Finally, a total of 22 studies containing 2,670 lymph nodes (LNs) that enrolled participants with suspicious neck LNs during thyroid nodule workup or papillary thyroid cancer (PTC) follow-up were included. In our analysis, the overall pooled sensitivity for FNA-Tg was 0.91 (95%CI: 0.87-0.93), specificity was 0.94 (95% CI: 0.91-0.96). Meta regression revealed that the cutoff value and status of serum Tg were sources of heterogeneity for sensitivity, and the cutoff value was source of heterogeneity for specificity. Additionally, the cutoff value and status of serum Tg were sources of heterogeneity in the joint model. Subgroup analysis about cut-off value showed that the choice of 1 ng/mL had highest sensitivity, 40 ng/mL had highest specificity. At last, we arrived at the conclusion that FNA-Tg measurement had high specificity and sensitivity in the early detection of LNs metastases from PTC by our meta-analysis. The technique was simple and could be recommended to apply in any FNA facility, especially when LN were small-sized. Significantly, a better standardization of criteria for FNA-Tg detection and cutoff value was required to provide useful data and to improve management of PTC patients in the future.

Thyrotropin, but Not Thyroid-Stimulating Antibodies, Induces Biphasic Regulation of Gene Expression in Human Thyrocytes

Background: Thyrotropin (TSH) and thyroid-stimulating antibodies (TSAbs) activate TSH receptor (TSHR) signaling by binding to its extracellular domain. TSHR signaling has been studied extensively in animal thyrocytes and in engineered cell lines, and differences in signaling have been observed in different cell systems. We, therefore, decided to characterize and compare TSHR signaling mediated by TSH and monoclonal TSAbs in human thyrocytes in primary culture. Methods: We used quantitative reverse transcription-polymerase chain reaction to measure mRNA levels of thyroid-specific genes thyroglobulin (TG), thyroperoxidase (TPO), iodothyronine deiodinase type 2 (DIO2), sodium-iodide symporter (NIS), and TSHR after stimulation by TSH or two monoclonal TSAbs, KSAb1 and M22. We also compared secreted TG protein after TSHR activation by TSH and TSAbs using an enzyme-linked immunosorbent assay. TSHR cell surface expression was determined using fluorescence activated cell sorting (FACS). Results: We found that TSH at low doses increases and at high doses (>1 mU/mL) decreases levels of gene expression for TSHR, TG, TPO, NIS, and DIO2. The biphasic effect of TSH on signaling was not caused by downregulation of cell surface TSHRs. This bell-shaped biphasic dose-response curve has been termed an inverted U-shaped dose-response curve (IUDRC). An IUDRC was also found for TSH-induced regulation of TG secretion. In contrast, KSAb1- and M22-induced regulation of TSHR, TG, TPO, NIS, and DIO2 gene expression, and secreted TG followed a monotonic dose-response curve that plateaus at high doses of activating antibody. Conclusions: Our data demonstrate that the physiological activation of TSHRs by TSH in primary cultures of human thyrocytes is characterized by a regulatory mechanism that may inhibit thyrocyte overstimulation. In contrast, TSAbs do not exhibit biphasic regulation. Although KSAb1 and M22 may not be representative of all TSAbs found in patients with Graves' disease, we suggest that persistent robust stimulation of TSHRs by TSAbs, unrelieved by a decrease at high TSAb levels, fosters chronic stimulation of thyrocytes in Graves' hyperthyroidism.

Class III PI3K Vps34 Controls Thyroid Hormone Production by Regulating Thyroglobulin Iodination, Lysosomal Proteolysis, and Tissue Homeostasis

Background: The production of thyroid hormones [triiodothyronine (T3), thyroxine (T4)] depends on the organization of the thyroid in follicles, which are lined by a monolayer of thyrocytes with strict apicobasal polarity. This polarization supports vectorial transport of thyroglobulin (Tg) for storage into, and recapture from, the colloid. It also allows selective addressing of channels, transporters, ion pumps, and enzymes to their appropriate basolateral [Na⁺/I^- symporter (NIS), SLC26A7, and Na⁺/K⁺-ATPase] or apical membrane domain (anoctamin, SLC26A4, DUOX2, DUOXA2, and thyroperoxidase). How these actors of T3/T4 synthesis reach their final destination remains poorly understood. The PI 3-kinase isoform Vps34/PIK3C3 is now recognized as a main component in the general control of vesicular trafficking and of cell homeostasis through the regulation of endosomal trafficking and autophagy. We recently reported that conditional Vps34 inactivation in proximal tubular cells in the kidney prevents normal addressing of apical membrane proteins and causes abortive macroautophagy. Methods:Vps34 was inactivated using a Pax8-driven Cre recombinase system. The impact of Vps34 inactivation in thyrocytes was analyzed by histological, immunolocalization, and messenger RNA expression profiling. Thyroid hormone synthesis was assayed by ¹²⁵I injection and plasma analysis. Results:Vps34 conditional knockout (Vps34^cKO) mice were born at the expected Mendelian ratio and showed normal growth until postnatal day 14 (P14), then stopped growing and died at ∼1 month of age. We therefore analyzed thyroid Vps34^cKO at P14. We found that loss of Vps34 in thyrocytes causes (i) disorganization of thyroid parenchyma, with abnormal thyrocyte and follicular shape and reduced PAS⁺ colloidal spaces; (ii) severe noncompensated hypothyroidism with extremely low T4 levels (0.75 ± 0.62 μg/dL) and huge thyrotropin plasma levels (19,300 ± 10,500 mU/L); (iii) impaired ¹²⁵I organification at comparable uptake and frequent occurrence of follicles with luminal Tg but nondetectable T4-bearing Tg; (iv) intense signal in thyrocytes for the lysosomal membrane marker, LAMP-1, as well as Tg and the autophagy marker, p62, indicating defective lysosomal proteolysis; and (v) presence of macrophages in the colloidal space. Conclusions: We conclude that Vps34 is crucial for thyroid hormonogenesis, at least by controlling epithelial organization, Tg iodination as well as proteolytic T3/T4 excision in lysosomes.

The Pervasive Effects of ER Stress on a Typical Endocrine Cell: Dedifferentiation, Mesenchymal Shift and Antioxidant Response in the Thyrocyte

The endoplasmic reticulum stress and the unfolded protein response are triggered following an imbalance between protein load and protein folding. Until recently, two possible outcomes of the unfolded protein response have been considered: life or death. We sought to substantiate a third alternative, dedifferentiation, mesenchymal shift, and activation of the antioxidant response by using typical endocrine cells, i.e. thyroid cells. The thyroid is a unique system both of endoplasmic reticulum stress (a single protein, thyroglobulin represents the majority of proteins synthesized in the endoplasmic reticulum by the thyrocyte) and of polarized epithelium (the single layer of thyrocytes delimiting the follicle). Following endoplasmic reticulum stress, in thyroid cells the folding of thyroglobulin was disrupted. The mRNAs of unfolded protein response were induced or spliced (X-box binding protein-1). Differentiation was inhibited: mRNA levels of thyroid specific genes, and of thyroid transcription factors were dramatically downregulated, at least in part, transcriptionally. The dedifferentiating response was accompanied by an upregulation of mRNAs of antioxidant genes. Moreover, cadherin-1, and the thyroid (and kidney)-specific cadherin-16 mRNAs were downregulated, vimentin, and SNAI1 mRNAs were upregulated. In addition, loss of cortical actin and stress fibers formation were observed. Together, these data indicate that ER stress in thyroid cells induces dedifferentiation, loss of epithelial organization, shift towards a mesenchymal phenotype, and activation of the antioxidant response, highlighting, at the same time, a new and wide strategy to achieve survival following ER stress, and, as a sort of the other side of the coin, a possible new molecular mechanism of decline/loss of function leading to a deficit of thyroid hormones formation.

Expression of thyroglobulin by regulatory T cells in thyroid tissue

The follicles are the minimal functional unit of the thyroid; the morphology and the function of each follicle can vary significantly. However, the reasons for the apparent follicular heterogeneity are poorly understood. Some tissue-resident regulatory T cells (Tregs) have a special phenotype that expresses unique molecules related to local tissue and regulates the tissue functions. The aim of this study was to identify the phenotype of thyroid Tregs and the roles of thyroid Tregs in thyroid physiological regulation. Thyroid tissue and peripheral blood samples were obtained from patients with benign thyroid nodules. Microarray-based gene expression, flow cytometry, immunofluorescence microscopy, and functional analysis of thyroid Tregs were performed. Here, we demonstrated that human thyroid Tregs expressed high level of thyroglobulin (Tg), both gene and protein. The immunofluorescence microscopy of thyroid section showed that the FOXP3+Tg+ cells concentrated in some of the thyroid follicles, at the side of the thyroid follicle. The peripheral blood Tregs expressed minimal levels of Tg, and low levels of Tg could effectively induce peripheral blood Tregs to express Tg, which was independent of thyrotropin simulation. Furthermore, the Tg secreted freely from thyroid Tregs that negatively regulated some thyroid-related genes expression. Our results revealed that the thyroid Tregs was a distinct population of Tregs, which expressed high level of Tg. The thyroid Tregs regulate thyroid function by Tg that is paracrine from the cells.

Circulating Exosomes Activate Dendritic Cells and Induce Unbalanced CD4+ T Cell Differentiation in Hashimoto Thyroiditis

OBJECTIVE

This study explored whether circulating exosomes effectively participate in the inflammatory response in Hashimoto thyroiditis (HT).

DESIGN

Exosomes were extracted from the serum of 30 patients with HT and 30 healthy control (HC) subjects. The expression of thyroperoxidase (TPO), thyroglobulin, high mobility group box 1 (HMGB1), heat shock protein 60 (HSP60), major histocompatibility complex class II (MHC-II), and intercellular adhesion molecule 1 (ICAM1) in exosomes was determined by Western blotting. Flow cytometry and immunofluorescence were performed to confirm that exosomes were taken up by healthy peripheral blood mononuclear cells (PBMCs) and dendritic cells (DCs). Then, either DCs or PBMCs were stimulated with HT exosomes (serum exosomes from patients with HT) or HC exosomes (serum exosomes from HC subjects) in the presence or absence of Toll-like receptor (TLR)2/3 inhibitors.

RESULTS

TPO, HSP60, and MHC-II expression was higher in HT exosomes than in HC exosomes. Exosomes were mainly taken up by CD14+ monocytes and CD11c+ DCs. After DCs were stimulated by HT exosomes, significant elevations were observed in MyD88, TRIF, and p-P65 expression; median fluorescence intensity of CD40 and CD83; and IL-6 production. After stimulating PBMCs with HT exosomes, CD11c+TLR2+/TLR3+ and CD4+IFN-γ+Th1/IL-17A+Th17A cell percentages were significantly elevated, and CD4+CD25+Foxp3+ Treg cell percentage was significantly decreased. HT exosomes induced increased IL-17A and IFN-γ production, whereas IL-10 production was suppressed. However, addition of TLR2 or TLR3 inhibitor reversed most of the abovementioned results.

CONCLUSIONS

Our study demonstrates that HT exosomes can present antigens to DCs and bind TLR2/3, causing DC activation via the nuclear factor κB signaling pathway, leading to an imbalance in CD4+ T lymphocyte differentiation, and potentially contributing to HT onset.

Bipolar limbic expression of auto-immune thyroid targets: thyroglobulin and thyroid-stimulating hormone receptor

The associations between thyroid auto-immunity and neuro-psychiatric disorders are well-documented. However, there exists limited literature specifically linking auto-immune thyroid disease (AITD) to bipolar disorder (BD). Thus, we investigated the likely association between Hashimoto's disease and BD through the extra-thyroidal localisation of thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in limbic regions of normal and bipolar human adult brain. Further, we hypothesised that changes in thyroid expression in bipolar limbic cortex may contribute to mood dysregulation associated with BD. Immuno-chemistry and in-situ PCR were used to localise TSH-R/TG within the amygdala, cingulate gyrus and frontal cortex of normal (n = 5) and bipolar (n = 5) brains. Reverse-transcriptase qPCR provided fold-change differences in TSH-R gene expression. The results demonstrated reduced thyroid protein expression in bipolar limbic regions; these novel results correlate with other neuro-imaging reports that describe reduced cortico-limbic tissue volumes and neuro-physiological activity during BD. We also demonstrated TG-like proteins exclusive to bipolar amygdala neurons, and which relates to previous neuro-imaging studies of amygdala hyperactivity and enhanced emotional sensitivity in BD. Indeed, reduced TSH-R/TG in limbic regions may predispose to, or bear relevance in the pathophysiology of mood dysregulation and symptoms of BD. Further, we attribute mood dysregulation in BD to limbic-derived TSH-R, which probably provides potential targets for thyroid auto-immune factors during Hashimoto's disease. Consequently, this may lead to inactivated and/or damaged neurons. The neuro-pathology of diminished neuronal functioning or neuronal atrophy suggests a novel neuro-degeneration mechanism in BD.

Increased Anaplastic Lymphoma Kinase Activity Induces a Poorly Differentiated Thyroid Carcinoma in Mice

Background: Radioiodine refractory dedifferentiated thyroid cancer is a major clinical challenge. Anaplastic lymphoma kinase (ALK) mutations with increased ALK activity, especially fusion genes, have been suggested to promote thyroid carcinogenesis, leading to development of poorly differentiated thyroid carcinoma (PDTC) and anaplastic thyroid carcinoma. To determine the oncogenic potential of increased ALK activity in thyroid carcinogenesis in vivo, we studied mice with thyrocyte-specific expression of a constitutively active ALK mutant. Methods: Mice carrying a Cre-activated allele of a constitutively active ALK mutant (F1174L) were crossed with mice expressing tamoxifen-inducible Cre recombinase (CreER^T2) under the control of the thyroglobulin (Tg) gene promoter to achieve thyrocyte-specific expression of the ALK mutant (ALK^F1174L mice). Survival, thyroid hormone serum concentration, and tumor development were recorded. Thyroids and lungs were studied histologically. To maintain euthyroidism despite dedifferentiation of the thyroid, a cohort was substituted with levothyroxine (LT4) through drinking water. Results: ALK^F1174L mice developed massively enlarged thyroids, which showed an early loss of normal follicular architecture 12 weeks after tamoxifen injection. A significant decrease in Tg and Nkx-2.1 expression as well as impaired thyroid hormone synthesis confirmed dedifferentiation. Histologically, the mice developed a carcinoma resembling human PDTC with a predominantly trabecular/solid growth pattern and an increased mitotic rate. The tumors showed extrathyroidal extension into the surrounding strap muscles and developed lung metastases. Median survival of ALK^F1174L mice was significantly reduced to five months after tamoxifen injection. Reduced Tg expression and loss of follicular structure led to hypothyroidism with elevated thyrotropin (TSH). To test whether TSH stimulation played a role in thyroid carcinogenesis, we kept ALK^F1174L mice euthyroid by LT4 substitution. These mice developed PDTC with identical histological features compared with hypothyroid mice, demonstrating that PDTC development was due to increased ALK activity and not dependent on TSH stimulation. Conclusion: Expression of a constitutively activated ALK mutant in thyroids of mice leads to development of metastasizing thyroid cancer resembling human PDTC. These results demonstrate in vivo that increased ALK activity is a driver mechanism in thyroid carcinogenesis.

A model of the cost of delaying treatment of Hashimotos thyroiditis: thyroid cancer initiation and growth

Hashimoto's thyroiditis (HT) is an autoimmune disorder that drives the function of thyroid gland to the sequential clinical states:euthyroidism (normal condition), subclinical hypothyroidism (asymptomatic period) and overt hypothyroidism (symptomatic period). In this disease, serum thyroidstimulating hormone (TSH) levels increase monotonically, stimulating the thyroid follicular cells chronically and initiating benign (non-cancerous) thyroid nodules at various sites of the thyroid gland. This process can also encourage growth of papillary thyroid microcarcinoma. Due to prolonged TSH stimulation, thyroid nodules may grow and become clinically relevant without the administration of treatment by thyroid hormone replacement. Papillary thyroid cancer (80% of thyroid cancer) whose incidence is increasing worldwide, is associated with Hashimoto's thyroiditis. A stochastic model is developed here to produce the statistical distribution of thyroid nodule sizes and growth by taking serum TSH value as the continuous input to the model using TSH values from the output of the patientspecific deterministic model developed for the clinical progression of Hashimoto's thyroiditis.

The cholesterol-derived metabolite dendrogenin A functionally reprograms breast adenocarcinoma and undifferentiated thyroid cancer cells

Dendrogenin A (DDA) is a tumor suppressor mammalian cholesterol-derived metabolite and a new class of ligand of the Liver X receptor (LXR), which displays tumor cell differentiation. In human MCF7 breast adenocarcinoma cells, DDA-induced cell differentiation was associated with an increased accumulation of neutral lipids and proteins found in milk indicating that DDA re-activates some functions of lactating cells. Active iodide transport occurs in the normal lactating mammary cells through the sodium/iodide symporter (NIS) and iodide (I) is secreted into milk to be used by the nursing newborn for thyroid hormones biosynthesis. In the present study, we assessed whether DDA may induce other characteristic of lactating cells such as NIS expression and iodine uptake in MCF7 breast cancer cells and extended this study to the papillary B-CPAP and undifferentiated anaplastic 8505c thyroid cancer cells. Moreover, we evaluated DDA impact on the expression of thyroid specific proteins involved in thyroid hormone biogenesis. We report here that DDA induces NIS expression in MCF7 cells and significantly increases the uptake of 131-I by acting through the LXR. In addition, DDA induces phenotypic, molecular and functional characteristics of redifferentiation in the two human thyroid carcinoma cell lines and the uptake of 131-I in the undifferentiated 8505c cells was associated with a strong expression of all the specific proteins involved in thyroid hormone biosynthesis, TSH receptor, thyroperoxidase and thyroglobulin. 131-I incorporation in the 8505c cells was stimulated by DDA as well as by the synthetic LXR ligand, GW3965. Together these data show that the re-differentiation of breast and thyroid cancer cells by DDA, is associated with the recovery of functional NIS expression and involves an LXR-dependent mechanism. These results open new avenues of research for the diagnosis of thyroid cancers as well as the development of new therapeutic approaches for radioiodine refractory thyroid cancers.

Structure of the saxiphilin:saxitoxin (STX) complex reveals a convergent molecular recognition strategy for paralytic toxins

Dinoflagelates and cyanobacteria produce saxitoxin (STX), a lethal bis-guanidinium neurotoxin causing paralytic shellfish poisoning. A number of metazoans have soluble STX-binding proteins that may prevent STX intoxication. However, their STX molecular recognition mechanisms remain unknown. Here, we present structures of saxiphilin (Sxph), a bullfrog high-affinity STX-binding protein, alone and bound to STX. The structures reveal a novel high-affinity STX-binding site built from a "proto-pocket" on a transferrin scaffold that also bears thyroglobulin domain protease inhibitor repeats. Comparison of Sxph and voltage-gated sodium channel STX-binding sites reveals a convergent toxin recognition strategy comprising a largely rigid binding site where acidic side chains and a cation-π interaction engage STX. These studies reveal molecular rules for STX recognition, outline how a toxin-binding site can be built on a naïve scaffold, and open a path to developing protein sensors for environmental STX monitoring and new biologics for STX intoxication mitigation.

Effects of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and triphenyl phosphate (TPP) on sex-dependent alterations of thyroid hormones in adult zebrafish

Organophosphate flame retardants (OPFRs) have been widely used as alternatives to polybrominated diphenyl ethers for fire prevention. OPFRs are suspected of causing potential thyroid disruption in humans. In fish, their thyroid hormone modulation is reported but the mechanisms of this modulation are less understood. Thyroid-disturbing effects of OPFRs were evaluated using adult zebrafish (Danio rerio) following 14d exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) or triphenyl phosphate (TPP). Plasma concentrations of thyroid hormones were measured and transcriptions of several genes involved in thyroid function were quantified in brain, thyroid, and liver. Exposure to TDCPP or TPP led to significant decreases in plasma triiodothyronine (T3) and thyroxine (T4) concentrations in the male fish, while the increases were observed in the female fish. Exposure to the OPFRs also altered the transcription of regulatory genes and receptors in hypothalamus, pituitary, and thyroid of the fish in sex-dependent manner. In the male fish, transcriptions of corticotropin-releasing hormone (crh) and thyroid-stimulating hormone (tsh) in the brain were significantly up-regulated, probably as a compensation for hypothyroidism, but thyroglobulin (tg) and deiodinase 2 (dio2) were down-regulated in thyroid or liver. In contrast, in the females, transcriptions of crh and tsh genes were significantly down-regulated. These observations show that TDCPP and TPP exposure can lead to sex-dependent disruptions of thyroid hormone balances in the adult zebrafish through alterations of the hypothalamus-pituitary-thyroid (HPT) axis.

ER stress contributes to high-fat diet-induced decrease of thyroglobulin and hypothyroidism

Recent studies revealed the emerging role of excess uptake of lipids in the development of hypothyroidism. However, the underlying mechanism is largely unknown. We investigated the effect of high-fat diet (HFD) on thyroid function and the role of endoplasmic reticulum (ER) in HFD-induced hypothyroidism. Male Sprague-Dawley rats were fed with HFD or control diet for 18 wk. HFD rats showed an impaired thyroid function, with decreased thyroglobulin (Tg) level. We found the ER stress was triggered in HFD rat thyroid glands and palmitate-treated thyrocytes. Luminal swelling of ER in thyroid epithelial cells of HFD rats was also observed. The rate of Tg degradation increased in palmitate-treated thyrocytes. In addition, applying 4-phenyl butyric acid to alleviate ER stress in HFD rats improved the decrease of Tg and thyroid function. Withdrawal of the HFD improved thyroid function . In conclusion, we demonstrate that ER stress mediates the HFD-induced hypothyroidism, probably by impairing the production of Tg, and attenuation of ER stress improves thyroid function. Our study provides the understanding of how HFD induces hypothyroidism.

Falsely elevated thyroglobulin and calcitonin due to rheumatoid factor in non-relapsing thyroid carcinoma: A case report

RATIONALE

Thyroglobulin (Tg) is an accurate indicator of clinical outcome after total thyroidectomy in patients with differentiated thyroid carcinoma. Usually, Tg levels agree with whole body scan. However, in some patient, discordant results were found, often because of Tg immunoassay interference. Several reports indicated that 2-site immunoassay interference with heterophile antibodies (HAb) can lead to misinterpretation of the laboratory test result.

PATIENT CONCERNS

We report a case of a 46-year-old woman referred to our endocrine clinic for markedly increased calcitonin (CT) without the associated clinical picture. The measurement was repeated with the same patient sample on a different analytical platform and the result was an undetectable CT level. The measurement of Tg was repeated on 3 different analytical platforms using chemiluminescence and electrochemiluminescence immunoassays and the results were different on each platform. HAb blocking tubes resulted in a different level of both CT and Tg, suggesting the presence of a heterophile substance in the serum sample. Further characterization showed reactivity to several animal species antibodies and an elevated level of the rheumatoid factor (RF).

DIAGNOSES

She was diagnosed as papillary thyroid carcinoma.

INTERVENTIONS

She had undergone thyroidectomy with lymph node dissection and radioactive therapy.

OUTCOMES

She was found not to have recurrence despite a high serum Tg level.

LESSONS

Our report illustrates a rare case of falsely elevated tumor markers levels due to assay interference caused by RF. This finding pointed out the importance of close communication between the clinician and laboratory staff in order to bring to light discordance between laboratory test results and clinical picture and avoid unnecessary diagnostic procedures and overtreatment.

Unidirectional transport of IgG by neonatal Fc receptor in human thyrocytes varies across different IgG subclasses

Neonatal Fc receptor (FcRn) is down-regulated in Hashimoto's thyroiditis (HT) thyrocytes and mediates IgG endocytosis in thyrocytes. The serum distribution of IgG subclasses (of TgAb and TPOAb) differs between HT patients and normal individuals. We aimed to explore the direction and regulation of FcRn-mediated IgG transport in thyrocyte monolayers and the difference between various IgG subclass transport. IgG was transported by FcRn from the basolateral to apical side in the thyrocyte monolayers grown on Transwell filters and the transport was inhibited by IFN-γ and TNF-α. Stimulation by T3 and TSH down-regulated FcRn expression in thyrocytes. IgG1 was transported preferentially over IgG2 and IgG4, which might be related to the differences in FcRn-binding affinities as shown by SPR. FcRn mediates unidirectional IgG transport in thyrocytes in a tissue-specific manner. Down-regulation of FcRn is speculated to play a protective role in HT pathogenesis by mainly reducing IgG1 transport in thyrocytes.

Interferon-α Triggers Autoimmune Thyroid Diseases via Lysosomal-Dependent Degradation of Thyroglobulin

CONTEXT

Autoimmune thyroid diseases (AITDs) arise from complex interactions among genetic, epigenetic, and environmental factors. Thyroglobulin (TG) is a major susceptibility gene for both Graves disease and Hashimoto thyroiditis. Interferon-α (IFNα), a cytokine secreted during viral infections, has emerged as a key trigger of AITD. We have shown that IFNα upregulates TG transcription; however, how the upregulation of TG transcription by IFNα triggers AITD is still unknown.

OBJECTIVE

To evaluate how IFNα triggers AITD by testing its effects on TG processing.

DESIGN

We exposed human thyroid cells to IFNα and evaluated its effects on TG expression and processing.

RESULTS

Human thyroid cells exposed to INFα had increased levels of TG mRNA but reduced TG protein levels, indicating TG protein degradation. IFNα induced endoplasmic reticulum stress, but surprisingly, neither the use of chemical chaperones nor proteasome inhibitor prevented IFNα-induced TG degradation. IFNα also increased LysoTracker staining and autophagy flux measured by net light chain 3 (LC3)-II and p62 fluxes. In addition, expression of autophagy markers LC3 and autophagy-related gene 5 was higher in thyroid tissues from patients with AITD. Finally, blocking lysosomal degradation prevented IFNα-induced degradation of TG.

CONCLUSION

We have shown in this study IFNα-induced lysosomal-dependent degradation of TG in human thyroid cells. Our findings suggest that during viral infections, local thyroidal IFNα production can lead to lysosomal TG degradation, releasing pathogenic TG peptides that can trigger AITD.

Glycosylation in the Thyroid Gland: Vital Aspects of Glycoprotein Function in Thyrocyte Physiology and Thyroid Disorders

The key proteins responsible for hormone synthesis in the thyroid are glycosylated. Oligosaccharides strongly affect the function of glycosylated proteins. Both thyroid-stimulating hormone (TSH) secreted by the pituitary gland and TSH receptors on the surface of thyrocytes contain N-glycans, which are crucial to their proper activity. Thyroglobulin (Tg), the protein backbone for synthesis of thyroid hormones, is a heavily N-glycosylated protein, containing 20 putative N-glycosylated sites. N-oligosaccharides play a role in Tg transport into the follicular lumen, where thyroid hormones are produced, and into thyrocytes, where hyposialylated Tg is degraded. N-glycans of the cell membrane transporters sodium/iodide symporter and pendrin are necessary for iodide transport. Some changes in glycosylation result in abnormal activity of the thyroid and alteration of the metabolic clearance rate of hormones. Alteration of glycan structures is a pathological process related to the progression of chronic diseases such as thyroid cancers and autoimmunity. Thyroid carcinogenesis is accompanied by changes in sialylation and fucosylation, β1,6-branching of glycans, the content and structure of poly-LacNAc chains, as well as O-GlcNAcylation, while in thyroid autoimmunity the main processes affected are sialylation and fucosylation. The glycobiology of the thyroid gland is an intensively studied field of research, providing new data helpful in understanding the role of the sugar component in thyroid protein biology and disorders.

Slit2 Modulates the Inflammatory Phenotype of Orbit-Infiltrating Fibrocytes in Graves' Disease

Human CD34+ fibrocytes, circulating monocyte lineage progenitor cells, have recently been implicated in thyroid-associated ophthalmopathy (TAO), the ocular manifestation of Graves' disease (GD). Fibrocytes express constitutive MHC class II (MHC-2) and, surprisingly, thyroglobulin (Tg) and functional thyrotropin (TSH) receptor (TSHR). Underlying expression of these thyroid proteins is the autoimmune regulator protein (AIRE). Fibrocytes respond robustly to TSH and thyroid-stimulating Igs by generating extremely high levels of inflammatory cytokines, such as IL-6. In TAO, they appear to infiltrate the orbit, where they transition to CD34+ orbital fibroblasts (OF). There, they coexist with CD34- OF as a mixed fibroblast population (GD-OF). In contrast to fibrocytes, GD-OF express vanishingly low levels of MHC-2, Tg, TSHR, and AIRE. Further, the amplitude of IL-6 induction by TSH in GD-OF is substantially lower. The molecular basis for this divergence between fibrocytes and CD34+ OF remains uncertain. In this article, we report that Slit2, an axon guidance glycoprotein, is constitutively expressed by the CD34- OF subset of GD-OF. Culture conditioned medium (CM) generated by incubating with GD-OF and CD34- OF substantially reduces levels of MHC-2, Tg, TSHR, and AIRE in fibrocytes. Expression can be restored by specifically depleting CM of Slit2. The effects of CD34- OF CM are mimicked by recombinant human Slit2. TSH induces Slit2 levels in GD-OF by enhancing both Slit2 gene transcription and mRNA stability. These findings suggest that Slit2 represents a TSH-inducible factor within the TAO orbit that can modulate the inflammatory phenotype of CD34+ OF and therefore may determine the activity and severity of the disease.

Expression of thyroid-stimulating hormone receptors and thyroglobulin in limbic regions in the adult human brain

Expression of the human thyroid-specific proteins, thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in non-thyroid tissue is well-documented. TSH-R has been identified in the heart, kidney, bone, pituitary, adipose tissue, skin and astrocyte cultures. TG has been identified in the skin, thymus and kidney. However, none of those previous studies had identified TSH-R or TG in specific human brain regions. Previously, a pilot study conducted by our group on normal adult human brain demonstrated TSH-R and TG in cortical neurons and cerebral vasculature, respectively, within various brain areas. In the present study, we extend this investigation of thyroid proteins specifically in limbic regions of normal human brain. Forensic human samples of amygdalae, cingulate gyrii, frontal cortices, hippocampii, hypothalamii, and thalamii were obtained from five individuals who had died of causes unrelated to head injury and had no evidence of brain disease or psychological abnormality. Tissues were probed with commercial polyclonal antibodies against human TSH-R and TG which resulted in the significant demonstration of neuronal TSH-R in all limbic regions examined. Other novel results demonstrated TG in vascular smooth muscle of all limbic regions and in some neurons. Finding thyroid proteins in limbic areas of the human brain is unique, and this study demonstrates that cerebro-limbic localisation of thyroid proteins may have potential roles in neuro-psycho-pharmacology.

Iodinated TG in Thyroid Follicles Regulate TSH/TSHR Signaling for NIS Expression

Our previous research has suggested that high degree of iodinated thyroglobulin (TG) may inhibit the expression and function of sodium iodide symporter (NIS), but the underlying mechanism remains unclear. In present study, we discuss a newly constructed follicle model in vitro, which was used to simulate the follicular structure of the thyroid and explore the regulatory roles of iodinated TG in the follicular lumen on NIS expression. The results showed that both NIS expression and PKA activity were increased in lowly iodinated TG group, while decreased NIS expression with increased PKC activity was found in highly iodinated TG group. Also, NIS expression was increased in PKA agonist-treated group, while decreased NIS was found in PKC agonist-treated group. Moreover, when the PLC-PKC pathway was blocked by PKC-specific inhibitor, highly iodinated TG significantly promoted the expression of NIS. However, when the cAMP-PKA pathway was blocked by a PKA-specific blocker, highly iodinated TG slightly suppressed NIS expression. TG with a low degree of iodination had the reverse effect on NIS. When the PLC-PKC pathway was blocked, TG with a low degree of iodination slightly promoted NIS expression. However, when the cAMP-PKA pathway was blocked, TG with a low degree of iodination greatly inhibited NIS expression. All these suggested that iodinated TG inhibited the expression of NIS by PLC-PKC pathway and promoted NIS expression via the cAMP-PKA pathway. When highly iodinated TG was present, the PLC-PKC pathway became dominant. In the presence of lowly iodinated TG, the cAMP-PKA became the major pathway.