Thyroid Follicular Cell Function Research Articles

Progress in the research of negative feedback effect of thyroglobulin

Thyroglobulin is the most important and abundant protein in thyroid follicles and has been widely studied as a tumor marker of thyroid cancer recurrence and persistence. Tg is considered the material basis of thyroid hormone synthesis and does not participate in the regulation of thyroid hormone synthesis and secretion. This review summarizes the recent progress in the research of thyroid hormone synthesis and secretion regulation via a negative feedback regulation mechanism by the thyroid-hypothalamus-pituitary axis. Thyroglobulin can negatively regulate the synthesis of thyroid hormone by thyroid follicular cells and antagonize the positive regulation of thyrotropin TSH. The function of thyroid follicular cells is presumably a result of Tg and TSH interaction, and a follicular cycle model is proposed to explain the causes of follicular heterogeneity in glands. We also discuss the prospects and clinical significance of studies into the negative feedback regulation mechanism of the thyroid-hypothalamus-pituitary axis and compare two theories for this mechanism.

Ginkgo biloba, friend or foe of thyroid follicular cells of adult male albino rats

Background Extract from the leaves of the Ginkgo biloba tree are used as a herbal remedy and dietary supplement. Numerous studies have suggested its therapeutic activity against many health disorders. However, it was found to be associated with histological changes in some organs. Recently, increased awareness about its safety and the potential hazards associated with its use were spotlighted. Aim The goal of the study was to assess the impact of G. biloba extract (GBE) on the histological structure and function of thyroid follicular cells of adult male albino rats. Materials and methods Thirty rats were categorized into three equal groups: group I, group II, and group III. Animals of group I were given distilled water and served as controls. GBE was given (100 mg/kg) orally for 4 and 6 weeks to group II and group III rats, respectively. At the designated times of the study, blood samples were taken for determination of serum triiodothyronine, thyroxin, and thyroid stimulating hormone. Rats were then euthanized, and thyroid lobes were processed for both light and electron microscopic examinations. Results The groups of animals exposed to GBE experienced histological changes in the follicular cells. These lesions included hypertrophy and hyperplasia of follicular cells. Group II showed evidence of hypertrophy wherein the follicles were lined with tall columnar cells. Nevertheless, group III showed many follicles lined with more than one layer of cells, along with colloid depletion. Ultrastructurally, dilated rough endoplasmic reticulum and swollen disrupted mitochondria as well as nuclear changes were further encountered in both groups. These histological changes were accompanied by alteration in the measured hormonal levels. Conclusion The study concluded that GBE administration to albino rats, either for 4 or for 6 weeks, caused alteration of thyroid follicular cell structure and function.

Прогностическое значение экспрессии натрий-йодного симпортера для высокодифференцированного рака щитовидной железы

The clue function of thyroid follicular cells is iodide (I) uptake and thyroid hormones production. NIS mediates the active transport of I into the thyroid follicular cells. It is impossible to perform effective 131 I radioablation ( 131 I RA) up to 10% of all differentiated thyroid cancer (DTC) owing to dedifferentiation and lost ability to cumulate I. To distinguish this group of patient preoperatively is difficult. Aim . To assess the utility of using membrane located NIS detection as marker of unfavorable prognosis for DTC after 131 I RA. Materials and methods . We enrolled in our study retrospectively sixty patients with DTC operated from 2005 to 2008. Based on postop routine histology examination we performed TNM staging. Forty-five patients received 131 I RA postoperatively. During 60 month of follow up recurrence were detected in 20 cases. In all 60 patients' level of membrane located NIS expression were detected immunohistochemicaly (IHC) in primary thyroid tumor. All statistical analysis performed using PC program Statistica 7.0. Results . We found that mean level of membrane located NIS expression in DTC is 4.5%, with maximum up to 10%, whereas mean level of NIS expression in normal tissue is 30—40%. Least mean level of NIS expression was in patients group with recurrence of DTC after 131 I RA (p=0.00083). We proved that crutial for recurrence of DTC after 131 I RA were decreased level of membrane located NIS expression less than 1%. As well as we found statistically significant correlation between Recurrence Free Survival (RFS) and level of NIS expression (p <0.005). Conclusion . Membrane location of NIS determines its functional activity, and membrane located NIS amount decreases in DTC. Detection of membrane located NIS in DTC has prognostic value.

Regulation of human thyroid follicular cell function by inhibition of vascular endothelial growth factor receptor signalling

The potential autocrine role of human thyroid vascular endothelial growth factors (VEGFs) was examined using the VEGF receptor (VEGFR) inhibitor, ZM306416HCl. ZM306416HCl reduced VEGFR2 phosphorylation and inhibited endogenous, steady-state levels of p42/44 MAPK phosphorylation. It potently inhibited the secretion of plasminogen activators (PA) and increased 125I uptake. Cell survival was compromised but rescued with insulin and TSH. Although the EGF receptor remained responsive to challenge by EGF in p42/44 MAPK assays, stimulatory effects of EGF on PA production were prevented by ZM306416HCl and those of protein kinase C stimulator, TPA reduced. In assays of 125I uptake, ZM306416HCl prevented the inhibitory effects of EGF but not those of TPA. We conclude that autocrine VEGF may modulate thyroid function and that VEGFR inhibition increases iodide uptake and decreases PA production through regulation of p42/44 MAPK phosphorylation. VEGFR inhibition may have effects on thyroid function which may contribute to “off target” effects in clinical trials.

Ghrelin potentiates TSH-induced expression of the thyroid tissue-specific genes thyroglobulin, thyroperoxidase and sodium-iodine symporter, in rat PC-Cl3 Cells

Ghrelin is a 28-amino-acid peptide that stimulates pituitary growth-hormone secretion and modulates food-intake and energy metabolism in mammals. It is mainly secreted by the stomach, but it is also expressed in many other tissues such as cartilage or the thyroid gland. In the present study we have analyzed by RT-PCR and using immunohistochemistry and immunofluorescence the expression and tissue distribution of ghrelin and its functional receptor (GHS-R type 1α) in thyroid cell-lines and in normal and pathological rat thyroid tissue. Additionally, by measuring the incorporation of BrdU, we have investigated if, as previously noted for FRTL-5 cells, ghrelin enhances the proliferation rate in the PC-Cl3 rat-thyrocyte cell-line. Finally, we have determined the stimulatory effect of ghrelin on TSH-induced expression of the tissue-specific key genes involved in the synthesis of thyroid hormone: thyroglobulin, thyroperoxidase and sodium–iodine symporter. Our data provide direct evidence that C-cell secreted ghrelin may be involved in the paracrine regulation of the thyroid follicular cell function.

Small molecule TSHR agonists and antagonists

TSH activates the TSH receptor (TSHR) thereby stimulating the function of thyroid follicular cells (thyrocytes) leading to biosynthesis and secretion of thyroid hormones. Because TSHR is involved in several thyroid pathologies, there is a strong rationale for the design of small molecule “drug-like” ligands. Recombinant human TSH (rhTSH, Thyrogen ®) has been used in the follow-up of patients with thyroid cancer to increase the sensitivity for detection of recurrence or metastasis. rhTSH is difficult to produce and must be administered by injection. A small molecule TSHR agonist could produce the same beneficial effects as rhTSH but with greater ease of oral administration. We developed a small molecule ligand that is a full agonist at TSHR. Importantly for its clinical potential, this agonist elevated serum thyroxine and stimulated thyroidal radioiodide uptake in mice after its absorption from the gastrointestinal tract following oral administration. Graves’ disease (GD) is caused by persistent, unregulated stimulation of thyrocytes by thyroid-stimulating antibodies (TSAbs) that activate TSHR. We identified the first small molecule TSHR antagonists that inhibited TSH- and TSAb-stimulated signalling in primary cultures of human thyrocytes. Our results provide proof-of-principle for effectiveness of small molecule agonists and antagonists for TSHR. We suggest that these small molecule ligands are lead compounds for the development of higher potency ligands that can be used as probes of TSHR biology with therapeutic potential.

Inhibitory action of the pineal gland on the nuclear volume of thyroid follicular cells in male gerbils (Meriones unguiculatus).

Karyometric investigations of thyroid follicular cells were performed in four groups of adult male gerbils [I. sham-operated (Sham PX) + short photoperiod (SPP)-exposed; II. Sham PX + long photoperiod (LPP)-exposed; III. pinealectomized (PX) + SPP-exposed; IV. PX + LPP-exposed]. The mean nuclear volume (MNV) of thyroid follicular cells was significantly higher in both PX groups (III and IV) when compared to Sham PX controls (I and II). In Sham PX gerbils the maintenance of animals in SPP (10 h light: 14 h darkness) for 13 weeks resulted in significant decrease of MNV of thyroid follicular cells in comparison to that in Sham PX animals kept in LPP (14 h light: 10 h darkness). Lighting conditions did not significantly affect the MNV of thyroid follicular cells in PX gerbils. These data suggest that the pineal gland itself and not light deprivation is the most important factor depressing the activity of the thyroid in male gerbils. Lighting conditions seem to affect the function of thyroid follicular cells inasmuch as they activate or block the action of the pineal gland.

Thyroid follicular cell function after non-lethal complement membrane attack

Terminal complement complexes have been identified around thyroid follicles in Graves' disease and Hashimoto's thyroiditis, and the concentrations of such complexes are increased in the sera of these patients, suggesting a role for complement activation and membrane attack complexes (MAC) in autoimmune thyroiditis. This has been investigated further using cultured human and rat thyroid cells. Thyrocytes were resistant to lysis by homologous complement, in contrast to the effects of heterologous (rabbit) complement. The formation of non-lethal amounts of MAC, using reactive lysis or classical pathway activation, significantly reduced cAMP production by these cells in response to thyroid-stimulating hormone (TSH) (P less than 0.01); similar effects were seen with thyroid-stimulating antibodies. Thyroid cells were able to recover rapidly from complement attack after washing and incubation for 30 min. Non-lethal MAC formation also resulted in reactive oxygen metabolite production, detected by luminol-dependent chemiluminescence in three out of five thyroid cell preparations tested. Ionomycin, but not TSH, also stimulated reactive oxygen metabolite production. These results suggest that repeated or continuous sub-lethal complement attack on thyroid cells may exacerbate hypothyroidism in Hashimoto's thyroiditis, or partially counter the effects of thyroid-stimulating antibodies in Graves' disease. Furthermore, the production of reactive oxygen metabolites in these circumstances could increase the intra-thyroidal inflammatory response; oxygen radical scavenging by anti-thyroid drugs (which are concentrated by thyrocytes) may account in part for the amelioration of thyroiditis observed with such treatment.

Quantitative High-Throughput Screening Using a Live-Cell cAMP Assay Identifies Small-Molecule Agonists of the TSH Receptor

The thyroid-stimulating hormone (TSH; thyrotropin) receptor belongs to the glycoprotein hormone receptor subfamily of 7-transmembrane spanning receptors. TSH receptor (TSHR) is expressed mainly in thyroid follicular cells and is activated by TSH, which regulates the growth and function of thyroid follicular cells. Recombinant TSH is used in diagnostic screens for thyroid cancer, especially in patients after thyroid cancer surgery. Currently, no selective small-molecule agonists of the TSHR are available. To screen for novel TSHR agonists, the authors miniaturized a commercially available cell-based cyclic adenosine 3',5' monophosphate (cAMP) assay into a 1536-well plate format. This assay uses an HEK293 cell line stably transfected with the TSHR coupled to a cyclic nucleotide gated ion channel as a biosensor. From a quantitative high-throughput screen of 73,180 compounds in parallel with a parental cell line (without the TSHR), 276 primary active compounds were identified. The activities of the selected active compounds were further confirmed in an orthogonal homogeneous time-resolved fluorescence cAMP-based assay. Forty-nine compounds in several structural classes have been confirmed as the small-molecule TSHR agonists that will serve as a starting point for chemical optimization and studies of thyroid physiology in health and disease.

USF Inhibits Cell Proliferation through Delay in G2/M Phase in FRTL-5 Cells

Upstream stimulatory factor (USF) has a negative effect on the cell proliferation in some cell types. However, its effect on thyrocytes is not clear. Therefore, we investigated the effects of USF on the proliferation and function of thyroid follicular cells. Complementary DNAs of the USF-1 and USF-2 were synthesized using RT-PCR from FRTL-5 cells, and each was transfected to FRTL-5 cells and papillary thyroid carcinoma cell lines. Cyclic AMP (cAMP) production and [methyl-3H] thymidine uptake after thyroid stimulating hormone (TSH) treatment were measured in FRTL-5 cells. In the carcinoma cell lines, 5-bromo-2'-deoxyuridine (BrdU) uptake was assayed to evaluate cell proliferation. Apoptosis was tested by Hoechst staining and cell cycle analysis was done using a fluorescence activated cell sorting. Expression of cell cycle regulating genes was evaluated by Northern and Western blotting. Overexpression of USF-1 and USF-2 significantly suppressed TSH-stimulated [methyl-3H] thymidine uptake (p<0.05), while it maintained TSH-stimulated cAMP production in FRTL-5 cells. Overexpression of USF significantly suppressed BrdU uptake in each carcinoma cell line, NPA and TPC-1 cells (p<0.05). It induced delay of cell cycle at the G2/M phase, but did not increase apoptosis in FRTL-5 cells. It was accompanied by a decrease of cyclin B1 and cyclin-dependent kinase (CDK)-1, and an increase of p27 expression. USF-1 and USF-2 suppressed cell proliferation of normal thyrocytes and thyroid carcinoma cells. However, they retained the ability to produce cAMP after TSH stimulation. Their inhibitory effect on cell proliferation might be caused partly by the delay in G2/M phase.

Ghrelin localization in rat and human thyroid and parathyroid glands and tumours

Ghrelin, the endogenous ligand of the growth hormone secretagogue receptor (GHS-R), is a 28 amino acid peptide originally isolated from rat stomach that has been primarily involved in the central neuroregulation of GH secretion and food intake. Previous studies demonstrated that ghrelin has a widespread expression in different normal cells and tissues, as well as in gastric, thyroid, testicular, breast and lung neoplasias. In the current study, we use molecular biology to detect ghrelin transcripts expression in rats, and immunohistochemical techniques to investigate the cellular distribution of this peptide in rat and human thyroid and parathyroid glands and tumours. Ghrelin was localized in thyroid C cells and in parathyroid cells. Thyroid carcinomas (medullar, follicular and papillary) and parathyroid adenomas also showed intense and diffuse immunostaining for ghrelin. These data provide direct morphological evidence that ghrelin may well be acting in a paracrine fashion in the regulation of thyroid follicular cell function. The diffuse ghrelin immunostaining found in the parathyroid gland opens up the possibility of its secretion to the bloodstream or its involvement in the regulation of the parathyroid function. Overall, expression of ghrelin in human and rat thyroid and parathyroid glands is highly suggestive of a conserved role of this molecule in the regulation of thyroid and parathyroid cell function.

Thyroglobulin gene mutations and other genetic defects associated with congenital hypothyroidism

Congenital hypothyroidism affects about 1:3000-1:4000 infants. Screening programs now permit early recognition and treatment, thus avoiding the disastrous consequences of thyroid hormone deficiency on brain development. In about 85%, congenital hypothyroidism is associated with developmental defects referred to as thyroid dysgenesis. They include thyroid (hemi)agenesis, ectopic tissue and thyroid hypoplasia. Thyroid dysgenesis is usually sporadic; in only 2% it occurs in a familial fashion. It can be caused by mutations in transcription factors that are essential for the development and function of thyroid follicular cells. Thyroid hypoplasia can also result from resistance to TSH at the level of the thyrocytes. Defects in the steps required for thyroid hormone synthesis within thyroid follicular cells are referred to as dyshormonogenesis and account for about 10-15% of congenital hypothyroidism. In contrast to thyroid dysgenesis, affected patients typically present with goitrous enlargement of the thyroid. The defects leading to dyshormonogenesis typically display a recessive mode of inheritance. Careful clinical, biochemical and molecular analyses of patients with syndromic and non-syndromic forms of thyroid dysgenesis and dyshormonogenesis have significantly enhanced our understanding of the wide spectrum of pathogenetic mechanisms underlying congenital hypothyroidism and provide unique insights into the (patho)physiology of thyroid development and hormone synthesis.

Regulation of Thyroid Follicular Cell Function by Intracellular Redox-Active Copper

Regulation of Thyroid Follicular Cell Function by Intracellular Redox-Active Copper

Regulation of thyroid follicular cell function by intracellular redox-active copper.

Pyrrolidine dithiocarbamate (PDTC) is a metal-chelating compound that exerts prooxidant or antioxidant effects and is widely used to study redox regulation of cell function. In the present study, we investigated effects of PDTC on the function of rat thyroid follicular FRTL-5 cells. Treatment of the cells with PDTC resulted in a marked decrease in Pax-8 messenger RNA level and its DNA-binding activity. This decrease was associated with a significant reduction in thyroperoxidase (TPO) messenger RNA level. Expression of TTF-1 and thyroglobulin was not affected by PDTC. Treatment with PDTC also decreased DNA-binding activity of p53, a tumor suppressor protein, and increased cell proliferation rates. These changes were not observed by the treatment with another antioxidant, N-acetyl-L-cysteine, suggesting that the metal-chelating, prooxidant property of PDTC is responsible for its effects. Indeed, the intracellular level of copper was significantly increased by PDTC. Treatment with bathocuproinedisulfonic acid, a noncell-permeable chelator of Cu1+, abrogated the copper increase by PDTC and its effects on Pax-8 and TPO expression as well as on p53 binding. Taken together, these results indicate that the intracellular level of redox-active copper is crucial for Pax-8 and TPO expression and for proliferation of thyroid follicular cells.

The effect of fasting and refeeding on thyroid follicule structure and thyroid hormone levels in young and old rats

In order to assess morphological and functional plasticity of the thyroid gland in aging the effects of fasting and refeeding on the thyroid morphology and thyroid hormone serum levels were compared with morphometry and RIA in young and old rats. Young (4 months) and old (24 months) male Wistar rats were fasted for 40 h and sampled, or fasted and fed thereafter for 4 or 24 h. In control (fed) old animals the thyroid follicules were larger, the follicular epithelium was smaller and colloid resorption was smaller than in young rats. ‘Thyroid activation index’ (epithelial volume/colloid volume ratio) was almost twice lower in the thyroids of control old rats. As the result of fasting, height, surface area and volume of epithelial follicular cells decreased in the thyroids of fasted young rats but not in old ones. On the contrary, in thyroids of fasted old rats the dimensions of epithelial cells did not change and thyroid colloid resorption was increased. After 24 h of refeeding, thyroid morphology in both young and old rats did not differ significantly as compared with control animals. Upon fasting, serum levels of thyroxine (T4) and triiodothyronine (T3) decreased by 28 and 38% in young and by 35 and 46% in old rats, respectively. However, T4 and T3 serum concentrations did not differ significantly between age groups in both fed and fasted states. During refeeding the increase in serum thyroxine concentration was delayed in old rats as compared with young ones. The results of morphological, morphometric and hormonal investigations indicate the existence of age-related changes in the structure and function of thyroid follicular cells.

Cytokines and thyroid function

Cytokines play a crucial role in autoimmune thyroid disease (ATD) through various mechanisms. They are produced in the thyroid by intrathyroidal inflammatory cells, in particular lymphocytes, as well as by the thyroid follicular cells (TFC) themselves and may thus act in a cascade to enhance the autoimmune process (Fig. 1). Cytokines upregulate the inflammatory reaction through stimulation of both T and B cells, resulting in antibody production and tissue injury. In addition, intrathyroidal cytokines induce immunological changes in TFC including enhancement of both major histocompatibility complex (MHC) class I and class II molecule expression, and upregulation of adhesion and complement regulatory molecule expression. Cytokines can also modulate both growth and function of TFC and have a role in extrathyroidal complications of ATD, most importantly thyroid-associated ophthalmopathy (TAO), where they induce fibroblast proliferation and enhance the production of glycosaminoglycans (GAG), resulting in proptosis and the other clinical features of the disease. In addition to these effects, exogenous administration of cytokines has been associated with impairment of thyroid function ranging from the appearance of autoantibodies alone to the development of frank thyroid dysfunction. Cytokines have also been implicated in subacute thyroiditis (SAT) and amiodarone-induced thyroid dysfunction, as well as in thyroid function abnormalities occurring in patients with non-thyroidal illnesses (NTI). Genetic variations in cytokine genes represent potential risk factors for ATD, and disease associations have been described for polymorphisms in IL-1ra and TNF beta genes. Recent experimental evidence suggests the possibility of novel cytokine-based therapeutic approaches for ATD and its complications, in particular TAO.

1,25-Dihydroxycholecalciferol modulates 3H-thymidine incorporation in FRTL5 cells.

1,25-dihydroxycholecalciferol (1,25(OH)2D3) possesses proliferation and differentiation modulating effects in many cell types in vitro. We studied the effect of 1,25(OH)2D3 on 3H-thymidine incorporation in FRTL5 cells, a cultured rat thyroid follicular cell line. 1,25(OH)2D3 alone at 10(-11) and 10(-9) M exerted no effect on 3H-thymidine incorporation. However, at 10(-7) M, 1,25(OH)2D3 slightly enhanced 3H-thymidine incorporation. In the presence of 5% calf serum, 1,25(OH)2D3 increased 3H-thymidine incorporation induced by calf serum in a dose-dependent manner. 1,25(OH)2D3 also enhanced 3H-thymidine incorporation induced by PMA, an extrinsic stimulator of protein kinase C, without directly affecting PMA-induced protein kinase C translocation. In contrast to the stimulatory effects of 1,25(OH)2D3 on the calf serum and PMA-induced 3H-thymidine incorporation, 1,25(OH)2D3 inhibited the increase in 3H-thymidine incorporation induced by TSH in a dose-dependent manner. This effect of 1,25(OH)2D3 on TSH-induced 3H-thymidine incorporation may be, in part, due to post-cAMP pathways since 1,25(OH)2D3 also inhibited the increase in 3H-thymidine incorporation induced by Bu2cAMP without affecting the TSH-induced increase in cAMP. The stimulatory effect of insulin on 3H-thymidine incorporation, a cAMP-independent process, was also inhibited by 1,25(OH)2D3. We conclude that 1,25(OH)2D3 affects 3H-thymidine incorporation in FRTL5 cells raising the possibility of a physiologic role for 1,25(OH)2D3 in the growth and function of thyroid follicular cells.