Two glycoprotein hormone subunits, (glycoprotein hormone α2-subunit GPA2) and (glycoprotein hormone β5-subunit GPB5) have been recently discovered which, when expressed in vitro, heterodimerize to form a new hormone called thyrostimulin. Thyrostimulin activates the thyroid-stimulating hormone receptor (TSHR) and has thyrotropic activity. Immunological studies have indicated that both subunits co-localize in pituitary cells. To explore the function of thyrostimulin in the rat, we have cloned rat GPA2 and GPB5, reconstituted the heterodimers in vitro, and confirmed that rat thyrostimulin activates TSHR with an affinity similar to that of TSH. In situ hybridization of the pituitary showed that while GPA2 is expressed in the anterior lobe, GPB5 is not detected in any of the lobes. A quantitative analysis showed that the co-localization of GPA2 and GPB5 is restricted in the rat to the eye and the testis. We found that GPB5 can be detected in the pituitary by quantitative-PCR, but at extremely low levels, 2000-fold lower than TSH β-subunit (GPBtsh). Furthermore, the levels of GPB5 remain constant during the estrus cycle, while those of GPA2 vary. Finally, we found that none of the thyrostimulin subunits was induced by TRH in pituitary cell culture. These data point at the thyrostimulin system as being functionally different to the TSH system.
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- Abstract: Thyroid* x
- Abstract: Digestion x
- Abstract: Thyroxine x
- Abstract: Thyroglobulin x
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- Abstract: Hypothyroidism x
- Abstract: Hyperthyroidism x
- Abstract: TSHR x
- Abstract: Metabolism x
Hiroshi Nagasaki, Zhiwei Wang, Valerie R Jackson, Steven Lin, Hans-Peter Nothacker and Olivier Civelli
Mihael Freamat and Stacia A Sower
The specificity of the vertebrate hypothalamic–pituitary–gonadal and hypothalamic–pituitary–thyroid axes is explained by the evolutionary refinement of the specificity of expression and selectivity of interaction between the glycoprotein hormones GpH (FSH, LH, and TSH) and their cognate receptors GpH-R (FSH-R, LH-R, and TSH-R). These two finely tuned signaling pathways evolved by gene duplication and functional divergence from an ancestral GpH/GpH-R pair. Comparative analysis of the protochordate and gnathostome endocrine systems suggests that this process took place prior or concomitantly with the emergence of the gnathostome lineage. Here, we report identification and characterization of a novel glycoprotein hormone receptor (lGpH-R II) in the Agnathan sea lamprey. This 781 residue protein was found ∼43% identical with mammalian TSH-R and FSH-R representative sequences, and similarly with these two classes of mammalian receptors it is assembled from ten exons. A synthetic ligand containing the lamprey glycoprotein hormone β-chain tethered upstream of a mammalian α-chain activated the lGpH-R II expressed in COS-7 cells but in a lesser extent than lGpH-R I. Molecular phylogenetic analysis of vertebrate GpH-R protein sequences suggests a closer relationship between lGpH-R II and gnathostome thyrotropin receptors. Overall, the presence and characteristics of the lamprey glycoprotein hormone receptors suggest existence of a primitive functionally overlapping glycoprotein hormone/glycoprotein hormone receptor system in this animal.
Limin Tian, Luyan Zhang, Jing Liu, Tiankang Guo, Cuixia Gao and Jing Ni
Recent studies have reported that subclinical hypothyroidism (SCH) is associated with atherosclerosis (AS). Thyroid hormone is maintained at normal levels in patients with SCH, whereas TSH is increased. However, the pathogenesis of AS in association with SCH is only partially understood. In addition, endothelial dysfunction plays an important role in the development of AS. The purpose of the present research was to study the direct effect of TSH on human umbilical vein endothelial cells (HUVECs). The expression of some genes associated with endothelial dysfunction after treatment with TSH was evaluated by real-time PCR and western blotting respectively. At first, we showed that the TSH receptor (TSHR) is expressed in HUVECs. We also provide evidence indicating that TSH treatment promotes tumor necrosis factor α-induced endothelial cells interactions by upregulating the expression of the adhesion molecules intercellular adhesion molecule-1. Furthermore, the expression of endothelial nitric oxide synthase (eNOS) and prostacyclin (PGI2) was significantly attenuated following treatment with TSH in dose- and time-dependent manner. Conversely, the results indicated that TSH upregulated endothelin-1 (ET1) mRNA and protein expression in HUVECs, similar effects were observed for plasminogen activator inhibitor-1 (PAI1) after treatment with various concentrations of TSH. Taken together, these results demonstrate that elevated TSH can promote endothelial dysfunction by altering gene expression in HUVECs.
Chen-Tian Shen, Wei-Jun Wei, Zhong-Ling Qiu, Hong-Jun Song, Xin-Yun Zhang, Zhen-Kui Sun and Quan-Yong Luo
More aggressive thyroid cancer cells show a higher activity of glycometabolism. Targeting cancer cell metabolism has emerged as a novel approach to prevent or treat malignant tumors. Glucose metabolism regulation effect of metformin in papillary thyroid cancer was investigated in the current study. Human papillary thyroid carcinoma (PTC) cell lines BCPAP and KTC1 were used. Cell viability was detected by CCK8 assay. Glucose uptake and relative gene expression were measured in metformin (0–10 mM for 48 h)-treated cells by 18F-FDG uptake assay and western blotting analysis, respectively. MicroPET/CT imaging was performed to detect 18F-FDG uptake in vivo. After treatment with metformin at 0, 2.5, 5 and 10 mM for 48 h, the ratio of p-AMPK to total AMPK showed significant rising in a dose-dependent manner in both BCPAP and KTC1, whereas p-AKT and p-mTOR expression level were downregulated. 18F-FDG uptake reduced after metformin treatment in a dose-dependent manner, corresponding to the reduced expression level of HK2 and GLUT1 in vitro. Xenograft model of PTC using BCPAP cells was achieved successfully. MicroPET/CT imaging showed that in vivo 18F-FDG uptake decreased after treatment with metformin. Immunohistochemistry staining further confirmed the reduction of HK2 and GLUT1 expression in the tumor tissue of metformin-treated PTC xenograft model. In conclusion, metformin could reduce glucose metabolism of PTC in vitro and in vivo. Metformin, by targeting glycometabolism of cancer cells, could be a promising adjuvant therapy alternative in the treatment modality of advanced thyroid carcinoma.
A. J. Pickles, N. Peers, W. R. Robertson and A. Lambert
The microheterogeneity of pituitary thyroid-stimulating hormone (TSH) is dependent on variations in the hormone's carbohydrate moieties. In this study, changes in the pattern of heterogeneity have been assessed by chromatofocusing, which separates the isospecies on the basis of their isoelectric points (pI). Rats (n = 6 per group) were either untreated or rendered hypo- or hyperthyroid by including in the drinking water either propylthiouracil (0·05% for 8 weeks) or thyroxine (T4; 4 mg/l for 6 weeks) before they were killed at 16 weeks. On autopsy, serum TSH and total T4 were (means±s.e.m.): 2±0·3 μg TSH/l and 64±5 nmol T4/l (control); <1 μg TSH/1 and 133±6 nmol T4/l (hyperthyroid); 58±6 μg TSH/1 and 32±6 nmol T4/l (hypothyroid). The pituitaries were individually homogenized and the TSH isoforms separated by chromatofocusing over a pH range of 7–4. Fractions were assayed for TSH by radioimmunoassay. TSH from the control group was distributed into seven major peaks with pI values of (means ±s.e.m., n=6) 6·9±0·1, 6·6±0·1, 6·2±0·1, 5·8±0·1, 5·5±0·1, 5·2±0·1 and 4·8±0·1; 7±3% of the TSH had a pI of <40. Six peaks of TSH were conserved in the hypothyroid group (with pI values of 6·8±0·1, 6·5±0·1, 6·2±0·1, 5·8±0·1, 5·4±0·1 and 5·2±0·1), and 11±4% of the hormone had a pI of <40. In contrast to the other two groups, only one major peak (with a pI of 5·8±0·1) was detected in the pituitaries from the hyperthyroid group; 13 ± 5% of the TSH had a pI of <40. In the pH range of 5·5– 60, the per cent distribution of TSH was 58±15 (hyperthyroid) compared with 17 ± 3 (hypothyroid) and 22±3 (euthyroid). Above pH 6, only 25±13% of the TSH (hyperthyroid) was present compared with 46±5% (hypothyroid) and 45±5% (euthyroid). Below pH 5·5, the per cent distribution of TSH was 19±5 (hyperthyroid), 37±5 (hypothyroid) and 35±3 (euthyroid). In conclusion, both hyper- and hypothyroidism are associated with changes in the composition of pituitary TSH. This change was most marked in the hyperthyroid group, where there was a selective loss of several isoforms of TSH.
Ricardo Núñez Miguel, Jane Sanders, Jadwiga Furmaniak and Bernard Rees Smith
We have studied glycosylation patterns in glycoprotein hormones (GPHs) and glycoprotein hormone receptor (GPHR) extracellular domains (ECD) from different species to identify areas not glycosylated that could be involved in intermolecular or intramolecular interactions. Comparative models of the structure of the TSHR ECD in complex with TSH and in complex with TSHR autoantibodies (M22, stimulating and K1-70, blocking) were obtained based on the crystal structures of the FSH-FSHR ECD, M22-TSHR leucine-rich repeat domain (LRD) and K1-70-TSHR LRD complexes. The glycosylation sites of the GPHRs and GPHs from all species studied were mapped on the model of the human TSH TSHR ECD complex. The areas on the surfaces of GPHs that are known to interact with their receptors are not glycosylated and two areas free from glycosylation, not involved in currently known interactions, have been identified. The concave faces of GPHRs leucine-rich repeats 3–7 are free from glycosylation, consistent with known interactions with the hormones. In addition, four other non-glycosylated areas have been identified, two located on the receptors’ convex surfaces, one in the long loop of the hinge regions and one at the C-terminus of the extracellular domains. Experimental evidence suggests that the non-glycosylated areas identified on the hormones and receptors are likely to be involved in forming intramolecular or intermolecular interactions.
C Massart, J Gibassier, N Genetet, M L Raoul, M Baron, F Le Gall and C Lucas
We studied the lymphocyte-induced alterations in hormonal metabolism and the production of tumour necrosis factor α (TNF-α) during coculture of thyrocytes and autologous lymphocytes from 20 patients with Graves' disease and from five normal subjects. Thyroglobulin (Tg) mRNA was assessed by slot-blot analysis under TSH stimulation. Tg, tri-iodothyronine (T3) and cAMP secretion in the presence of TSH were measured by RIA after 3 or 5 days of coculture. TNF-α levels produced after 5 days incubation were also assayed in lymphocyte culture and coculture media.
Lymphocytes isolated from peripheral blood (PBLs) altered the production of Tg, T3 and cAMP in autologous thyrocytes. Intrathyroidal lymphocytes (ITLs) decreased Tg and cAMP secretion but had no effect on T3 secretion. The reductions in Tg and cAMP levels obtained with mechanically isolated ITLs (M-ITLs) were generally higher than those obtained with ITLs isolated by dispase (D-ITLs). No difference was seen between Graves' disease and normal cocultures. PBLs secreted large concentrations of TNF-α, larger than those obtained with M-ITLs whereas D-ITLs produced low amounts of this cytokine. In coculture, TNF-α levels were lower than those observed in lymphocyte culture. Significant correlations were obtained between TNF-α levels and the decrease in Tg, T3 and cAMP concentrations. The percentage of T lymphocytes was higher in PBLs and D-ITLs than in M-ITLs. B lymphocytes levels were higher in ITLs, especially M-ITLs, than in PBLs. TNF-α production by B lymphocytes was maximal in M-ITLs.
In conclusion, lymphocytes induced a decrease in hormonal thyroid metabolism when cocultured with autologous thyrocytes. These perturbations may be attributed, at least partly, to TNF-α secreted by lymphocytes. TNF-α interacts via the adenylate cyclase pathway of TSH signal transduction.
D Pasquali, GM Pierantoni, A Fusco, S Staibano, V Colantuoni, A De Bellis, A Bellastella and AA Sinisi
Expansion of adipose tissue in the orbits is a key feature of Graves' ophthalmopathy. Recent evidence shows that orbital fibroblasts are committed to differentiate into adipocytes under appropriate stimuli. Rosiglitazone, an agonist of the nuclear hormone receptor, peroxisome proliferator-activated receptor gamma (PPARgamma) is able to induce both differentiation of orbital fibroblasts into mature adipocytes and expression of the TSH receptor (TSHr) gene. Several studies have suggested an important role of the high mobility group AT-hook 2 (HMGA2) gene in adipocytic cell growth and development. To investigate further the association between adipogenesis-related genes and orbital fibroblasts, we treated fibroblasts from Graves' ophthalmopathy (FGOs) and from normal orbital tissues with fenofibrate, a specific agonist for PPARalpha. We then evaluated the expression of the PPARalpha, PPARgamma2, HMGA2, leptin and TSHr genes before and after 24 h of fenofibrate treatment, using semiquantitative and real-time PCR. For up to 96 h after exposure to fenofibrate, FGOs differentiated into adipocytes. PPARalpha and PPARgamma2 were expressed more in FGOs than in normal cultures, whereas TSHr mRNA was detected only in FGOs. Expression of HMGA2 mRNA and protein was significantly increased in FGOs from 6 to 24 h after fenofibrate, confirming its role in the early phase of adipocyte differentiation. Treatment with fenofibrate for 24 h significantly increased the expression of leptin and TSHr genes. Moreover, TSH treatment significantly increased the accumulation of cAMP, demonstrating that FGOs express functional TSHr. The high level of expression of PPARalpha other than PPARgamma2 transcripts and the stimulating effect of fenofibrate on adipogenesis and on HMGA2, leptin and TSHr genes also indicate that the PPARalpha pathway plays an important part in the adipocyte differentiation of FGOs. These findings suggest that novel drugs to antagonize PPARalpha, other than the PPARgamma signalling system, may also need to be considered in the treatment or prevention of Graves' ophthalmopathy.
L B Nicholson, H Vlase, P Graves, M Nilsson, J Molne, G C Huang, N G Morgenthaler, T F Davies, A M McGregor and J P Banga
We have characterized four murine monoclonal antibodies (mAbs) to the extracellular domain of the human TSH receptor (TSH-R.E), the target autoantigen of Graves' disease. Recombinant TSH-R.E used as immunogen, was produced in E. coli as a fusion protein with glutathione-S-transferase or in a baculovirus-insect cell system, as a non-fusion glycoprotein. To increase the epitope specificity of the mAbs, two different strains of mice (H-2b and H-2d) were immunized. The epitopes recognized by the mAbs were characterized by immunoblotting with various recombinant constructs of TSH-R.E and by binding to overlapping synthetic peptides of the receptor. The four IgG mAbs characterized recognized epitopes localized to different regions on the TSH-R.E; amino acids 22–35 (A10 and All, both IgG2b from H-2b animals), amino acids 402–415 (A7, IgG2b from H-2b animals) and amino acids 147–228 (A9, IgG1 from H-2d animals). Immunolocalization studies showed that mAb A9 recognized TSH-R.E on unfixed cryostat sections, where binding was localized to the basolateral plasma membrane of thyroid follicular cells, suggesting that this antibody reacts with the native receptor on thyroid cells. The binding of the mAbs A7, A10 and All was also restricted to the basal surface of thyroid cells, but only after acetone fixation of the sections, implying that the epitopes recognized on the amino and carboxyl terminus of the extracellular region of the receptor are not accessible on the native molecule. None of the mAbs stimulated cyclic AMP responses in COS-7 cells transiently transfected with full-length functioning TSH-R.E, whilst weak inhibition of binding of radiolabelled TSH to porcine membranes in a radioreceptor assay was apparent with mAb A10 and All, but only at high concentrations of IgG. The ability of mAb A9 to bind to the native receptor without stimulating activity or inhibition of TSH binding suggests that antibody can bind to the central region of the TSH-R.E without perturbing receptor function. The availability of mAbs that recognize epitopes on different regions of the extracellular domain of TSH-R will lead to a better understanding of the autoantigenic regions on TSH-R implicated in disease activity.
Karen Jesus Oliveira, Maria Isabel Chiamolera, Gisele Giannocco, Carmen Cabanelas Pazos-Moura and Tania Maria Ortiga-Carvalho
The modern concept of thyroid disruptors includes synthetic chemicals and bioactive compounds from food that interfere with any aspect of the hypothalamus–pituitary–thyroid axis, thyroid hormone biosynthesis and secretion, blood and transmembrane transport, metabolism and local actions of thyroid hormones. This review highlights relevant disruptors that affect populations through their diet: directly from food itself (fish oil and polyunsaturated fatty acids, pepper, coffee, cinnamon and resveratrol/grapes), through vegetable cultivation (pesticides) and from containers for food storage and cooking (bisphenol A, phthalates and polybrominated diphenyl ethers). Due to the vital role of thyroid hormones during every stage of life, we review effects from the gestational period to adulthood, including evidence from in vitro studies, rodent models, human trials and epidemiological studies.