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The thyroid maintains systemic homeostasis by regulating serum thyroid hormone concentrations. Here we report the establishment of three-dimensional (3D) organoids from adult thyroid tissue representing murine and human thyroid follicular cells (TFCs). The TFC organoids (TFCOs) harbor the complete machinery of hormone production as visualized by the presence of colloid in the lumen and by the presence of essential transporters and enzymes in the polarized epithelial cells that surround a central lumen. Both the established murine as human thyroid organoids express canonical thyroid markers PAX8 and NKX2.1, while the thyroid hormone precursor thyroglobulin is expressed at comparable levels to tissue. Single-cell RNA sequencing and transmission electron microscopy confirm that TFCOs phenocopy primary thyroid tissue. Thyroid hormones are readily detectable in conditioned medium of human TFCOs. We show clinically relevant responses (increased proliferation and hormone secretion) of human TFCOs toward a panel of Graves’ disease patient sera, demonstrating that organoids can model human autoimmune disease.

Thyroid hormones (thyroxine, T4, and triiodothyronine, T3) are indispensable for sustaining vertebrate life, and their deficiency gives rise to a wide range of symptoms characteristic of hypothyroidism, affecting 5–10% of the world’s population. The precursor for thyroid hormone synthesis is thyroglobulin (Tg), a large iodoglycoprotein consisting of upstream regions I-II-III (responsible for synthesis of most T4) and the C-terminal CholinEsterase-Like (ChEL) domain (responsible for synthesis of most T3, which can also be generated extrathyroidally by T4 deiodination). Using CRISPR/Cas9-mediated mutagenesis, we engineered a knock-in of secretory ChEL into the endogenous TG locus. Secretory ChEL acquires Golgi-type glycans and is properly delivered to the thyroid follicle lumen, where T3 is first formed. Homozygous knock-in mice are capable of thyroidal T3 synthesis but largely incompetent for T4 synthesis such that T4-to-T3 conversion contributes little. Instead, T3 production is regulated thyroidally by thyrotropin (TSH). Compared to cog/cog mice with conventional hypothyroidism (low serum T4 and T3), the body size of ChEL-knock-in mice is larger; although, these animals with profound T4 deficiency did exhibit a marked elevation of serum TSH and a large goiter, despite normal circulating T3 levels. ChEL knock-in mice exhibited a normal expression of hepatic markers of thyroid hormone action but impaired locomotor activities and increased anxiety-like behavior, highlighting tissue-specific differences in T3 versus T4 action, reflecting key considerations in patients receiving thyroid hormone replacement therapy.

The global effort to prevent iodine deficiency disorders through iodine supplementation, such as universal salt iodization, has achieved impressive progress during the last few decades. However, iodine excess, due to extensive environmental iodine exposure in addition to poor monitoring, is currently a more frequent occurrence than iodine deficiency. Iodine excess is a precipitating environmental factor in the development of autoimmune thyroid disease. Excessive amounts of iodide have been linked to the development of autoimmune thyroiditis in humans and animals, while intrathyroidal depletion of iodine prevents disease in animal strains susceptible to severe thyroiditis. Although the mechanisms by which iodide induces thyroiditis are still unclear, several mechanisms have been proposed: (1) excess iodine induces the production of cytokines and chemokines that can recruit immunocompetent cells to the thyroid; (2) processing excess iodine in thyroid epithelial cells may result in elevated levels of oxidative stress, leading to harmful lipid oxidation and thyroid tissue injuries; and (3) iodine incorporation in the protein chain of thyroglobulin may augment the antigenicity of this molecule. This review will summarize the current knowledge regarding excess iodide as an environmental toxicant and relate it to the development of autoimmune thyroid disease.

The thyroglobulin (TG) protein is essential to thyroid hormone synthesis, plays a vital role in the regulation of metabolism, development and growth and serves as intraglandular iodine storage. Its architecture is conserved among vertebrates. Synthesis of triiodothyronine (T 3 ) and thyroxine (T 4 ) hormones depends on the conformation, iodination and post-translational modification of TG. Although structural information is available on recombinant and deglycosylated endogenous human thyroglobulin (hTG) from patients with goiters, the structure of native, fully glycosylated hTG remained unknown. Here, we present the cryo-electron microscopy structure of native and fully glycosylated hTG from healthy thyroid glands to 3.2 Å resolution. The structure provides detailed information on hormonogenic and glycosylation sites. We employ liquid chromatography–mass spectrometry (LC-MS) to validate these findings as well as other post-translational modifications and proteolytic cleavage sites. Our results offer insights into thyroid hormonogenesis of native hTG and provide a fundamental understanding of clinically relevant mutations. The iodinated thyroglobulin functions as iodine storage and carrier protein and a precursor for thyroid hormone (TH) biogenesis. Here, the authors report the structure of native, fully glycosylated human thyroglobulin, revealing the location of the hTg hormonogenic and glycosylation sites.

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.

Papillary thyroid carcinoma (PTC) frequently involves cervical lymph node (LN) metastases and is a major determinant of prognosis and recurrence. However, cytology alone has limitations. Fine-needle aspiration thyroglobulin (FNA-Tg) has emerged as a promising diagnostic marker, although its cutoff value remains controversial, particularly in patients with thyroglobulin antibodies (TgAbs). We retrospectively analyzed 63 LNs of 60 patients with PTC at a single medical center. Patients underwent FNA-Tg measurements and concurrent cytological evaluation. Diagnostic performance metrics, including sensitivity, specificity, positive and negative predictive value, and overall accuracy, were evaluated; the cutoff value was determined; and the potential influence of factors such as TgAb on FNA-Tg levels was investigated. A cutoff value of 4.23 ng/mL for FNA-Tg achieved 100% sensitivity and 90.2% specificity, with an overall accuracy of 93.6%. TgAb positivity did not significantly affect the diagnostic performance in patients with FNA-Tg. FNA-Tg might be useful for detecting local LN recurrence and providing valuable diagnostic insights, particularly in patients with residual thyroid tissue or positive TgAbs.

The detection of thyroglobulin in lymph node (LN) fine needle aspirates (FNA-Tg) is an effective supplement to ultrasound and fine needle aspiration cytology (FNAC) in diagnosis of cervical LN metastases for patients with papillary thyroid carcinoma (PTC). However, there is no unique cutoff value of FNA-Tg in practice. We aimed to determine the optimal cutoff of FNA-Tg and evaluate the interfering factors of FNA-Tg. A serial of 405 lateral cervical LN samples from 317 patients with PTC were analyzed retrospectively. Receiver operating characteristic (ROC) curve was used to determine the optimal cutoff of FNA-Tg. The factors that impact FNA-Tg were evaluated. Serum Tg, serum thyroglobulin antibody (TgAb) and serum thyroid stimulating hormone (TSH) level, and thyroid status did not differ between the malignant and benign LN groups. The median FNA-Tg was 3.81 ng/mL (0.16–33.40 ng/mL) in LNs without metastasis and 310.32 ng/mL (124.41–500.00 ng/mL) in LNs with metastasis, and the differences reached statistical significance ( P  < 0.01). The optimal cutoff of FNA-Tg was 36.22 ng/mL, and the values of area under the curve (AUC), sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) was 0.88, 0.89, 0.75, 0.91 and 0.71, respectively. The diagnostic accuracy of FNA-Tg cutoff of 36.22ng/mL was 85%. When FNAC and the present FNA-Tg cutoff of 36.22 ng/mL were combined together, the diagnostic sensitivity, specificity, PPV, NPV and diagnostic accuracy was 0.96, 0.75, 0.92, 0.87 and 91%, respectively. FNA-Tg improves the diagnostic efficacy of FNAC for PTC lateral cervical LN metastasis, and the optimal cutoff value of FNA-Tg was 36.22 ng/mL. FNA-Tg was affected by LN status but was not associated with serum Tg, serum TgAb, serum TSH and thyroid status.

Iodine is essential in the biosynthesis of thyroid hormones that affect metabolic processes in the organism from the prenatal state to the elderly. The immediate indicator of iodine intake is the concentration of iodine in urine, but the indicator of iodine intake in the longer term of several months is thyroglobulin (Tg). Tg negatively correlated with increasing intake of iodine in population that do not suffer from thyroid disease, while a more than adequate to excessive iodine intake leads to an increase in Tg. The dependence of Tg on iodine can be described by a U-shaped curve. Thyroglobulin in serum is elevated in thyroid disease mainly in hyperthyroidism (diagnosis E05 of WHO ICD-10 codes) and in goiter (diagnosis E04 of WHO ICD-10 codes). Tg values decrease below 20 µg/l after effective treatment of patients with thyroid disease. Thyroglobulin may thus be an indicator of thyroid stabilization and the success of the thyroid gland treatment.

Thyroglobulin (Tg) is the macromolecular precursor of thyroid hormones and is thought to be uniquely expressed by thyroid epithelial cells. Tg and the thyroid-stimulating hormone receptor (TSHR) are targets for autoantibody generation in the autoimmune disorder Graves disease (GD). Fully expressed GD is characterized by thyroid overactivity and orbital tissue inflammation and remodeling. This process is known as thyroid-associated ophthalmopathy (TAO). Early reports suggested that in TAO, both Tg and TSHR become overexpressed in orbital tissues. Previously, we found that CD34+ progenitor cells, known as fibrocytes, express functional TSHR, infiltrate the orbit, and comprise a large subset of orbital fibroblasts in TAO. We now report that fibrocytes also express Tg, which resolves as a 305-kDa protein on Western blots. It can be immunoprecipitated with anti-Tg Abs. Further, 125iodine and [35S]methionine are incorporated into Tg expressed by fibrocytes. De novo Tg synthesis is attenuated with a specific small interfering RNA targeting the protein. A fragment of the Tg gene promoter fused to a luciferase reporter exhibits substantial activity when transfected into fibrocytes. Unlike fibrocytes, GD orbital fibroblasts, which comprise a mixture of CD34+ and CD34– cells, express much lower levels of Tg and TSHR. When sorted into pure CD34+ and CD34– subsets, Tg and TSHR mRNA levels become substantially higher in CD34+ cells. These findings indicate that human fibrocytes express multiple \"thyroid-specific\" proteins, the levels of which are reduced after they infiltrate tissue. Our observations establish the basis for Tg accumulation in orbital GD.

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.