Interaction of TSH, insulin and insulin-like growth factors in regulating thyroid growth and function

Transplantable human thyroid organoids generated from embryonic stem cells to rescue hypothyroidism

The thyroid gland captures iodide in order to synthesize hormones that act on almost all tissues and are essential for normal growth and metabolism. Low plasma levels of thyroid hormones lead to hypothyroidism, which is one of the most common disorder in humans and is not always satisfactorily treated by lifelong hormone replacement. Therefore, in addition to the lack of in vitro tractable models to study human thyroid development, differentiation and maturation, functional human thyroid organoids could pave the way to explore new therapeutic approaches. Here we report the generation of transplantable thyroid organoids derived from human embryonic stem cells capable of restoring plasma thyroid hormone in athyreotic mice as a proof of concept for future therapeutic development.

Metformin in Differentiated Thyroid Cancer: Molecular Pathways and Its Clinical Implications

Metformin is a synthetic biguanide that improves insulin sensitivity and reduces hepatic gluconeogenesis. Aside being the first-line therapy for Type 2 Diabetes (T2D), many pleiotropic effects have been discovered in recent years, such as its capacity to reduce cancer risk and tumorigenesis. Although widely studied, the effect of metformin on thyroid cancer remains controversial. Potential mechanisms for its growth inhibitory effects have been elucidated in various preclinical studies that involved pathways related to adenosine mono-phosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), mitochondrial glycerophosphate dehydrogenase (mGPDH), and the nuclear factor κB (NF-κB). Hyperinsulinemia increases cell glucose uptake and oxidative stress, and promotes thyroid cell growth, leading to hyperproliferation, carcinogenesis, and the development of malignant tumors. Furthermore, it has also been related to thyroid nodules size in nodular disease, as well as tumoral size in patients with thyroid cancer. Several clinical studies concluded that metformin might have an important role as an adjuvant therapy to reduce the growth of benign and malignant thyroid neoplasms. This suggests that metformin might be useful for patients with differentiated or poorly differentiated thyroid cancer and metabolic diseases such as insulin resistance or diabetes.

Insulin-Like Growth Factor Pathway and the Thyroid

The insulin-like growth factor (IGF) pathway comprises two activating ligands (IGF-I and IGF-II), two cell-surface receptors (IGF-IR and IGF-IIR), six IGF binding proteins (IGFBP) and nine IGFBP related proteins. IGF-I and the IGF-IR share substantial structural and functional similarities to those of insulin and its receptor. IGF-I plays important regulatory roles in the development, growth, and function of many human tissues. Its pathway intersects with those mediating the actions of many cytokines, growth factors and hormones. Among these, IGFs impact the thyroid and the hormones that it generates. Further, thyroid hormones and thyrotropin (TSH) can influence the biological effects of growth hormone and IGF-I on target tissues. The consequences of this two-way interplay can be far-reaching on many metabolic and immunologic processes. Specifically, IGF-I supports normal function, volume and hormone synthesis of the thyroid gland. Some of these effects are mediated through enhancement of sensitivity to the actions of TSH while others may be independent of pituitary function. IGF-I also participates in pathological conditions of the thyroid, including benign enlargement and tumorigenesis, such as those occurring in acromegaly. With regard to Graves' disease (GD) and the periocular process frequently associated with it, namely thyroid-associated ophthalmopathy (TAO), IGF-IR has been found overexpressed in orbital connective tissues, T and B cells in GD and TAO. Autoantibodies of the IgG class are generated in patients with GD that bind to IGF-IR and initiate the signaling from the TSHR/IGF-IR physical and functional protein complex. Further, inhibition of IGF-IR with monoclonal antibody inhibitors can attenuate signaling from either TSHR or IGF-IR. Based on those findings, the development of teprotumumab, a β-arrestin biased agonist as a therapeutic has resulted in the first medication approved by the US FDA for the treatment of TAO. Teprotumumab is now in wide clinical use in North America.

Subclinical hypothyroidism and the risk of cancer incidence and cancer mortality: a systematic review

BACKGROUND

Thyroid hormone has been shown to be involved in carcinogenesis via its effects on cell proliferation pathways. The objective of this study is to determine the association between subclinical hypothyroidism (SCH) and the risk of incident cancer and cancer mortality via systematic review.

METHODS

A systematic search was performed on Medline and Pubmed to identify relevant studies. Randomized controlled trials, and observational studies assessing SCH or its treatment and the risk of incident cancer or cancer mortality were identified.

RESULTS

A total of 7 cohort and 2 case-control studies met our inclusion criteria. In general, these studies were of medium to good quality. Overall, studies revealed no association between SCH and breast and prostate cancer. One study found that untreated SCH may be associated with an increased risk of colorectal cancer (adjusted odds ratio [OR]: 1.16; 95% confidence interval [CI]: 1.08-1.24). One study showed an increased risk in thyroid cancer incidence (adjusted OR: 3.38; 95% CI: 2.05-5.59) associated with elevation of a thyroid stimulating hormone (TSH) of > 1.64mIU/L. Two studies found an increase in cancer mortality among patients with SCH compared to euthyroid individuals; in contrast one study found no association between subclinical hypothyroidism and cancer mortality among aging men.

CONCLUSION

The number of studies examining thyroid dysfunction and cancer risk and mortality is limited. Future studies assessing the association between thyroid dysfunction and cancer risk and mortality are needed, which will further address the need to treat subclinical hypothyroidism.

Alteration of retinal metabolism and oxidative stress may implicate myopic eye growth: Evidence from discovery and targeted proteomics in an animal model

Myopia, the most common cause of impaired vision, may induce sight- threatening diseases or ocular complications due to axial elongation. The exact mechanisms underlying myopia development have received much attention and understanding of these is necessary for clinical prevention or therapeutics. In this study, quantitative proteomics using Isotope Coded Protein Label (ICPL) was applied to identify differentially regulated proteins in the retinas of myopic chicks and, from their presence, infer the possible pathogenesis of excessive ocular elongation. Newly hatched white leghorn chicks (n = 15) wore -10D and + 10D lenses bilaterally for 3 and 7 days, respectively, to develop progressive lens-induced myopia (LIM) and hyperopia (LIH). Retinal proteins were quantified with nano-liquid chromatography electrospray ionization coupled with tandem mass spectrometry (nanoLC-ESI-MS/MS). Bioinformatics analysis of differentially regulated proteins revealed that the majority originated from the cytoplasmic region and were related to various metabolic, glycolytic, or oxidative processes. The fold changes of four proteins of interest (vimentin, apolipoprotein A1, interphotoreceptor retinoid binding protein, and glutathione S-transferase) were further confirmed by a novel high-resolution multiple reaction monitoring mass spectrometry (MRM-HR) using a label-free approach. SIGNIFICANCE: Discovery of effective protein biomarkers of myopia has been extensively studied to inhibit myopia progression. This study first applied lens-induced hyperopia and myopia in the same chick to maximize the inter-ocular differences, aiming to discover more protein biomarker candidates. The findings provided new evidence that myopia was metabolism related, accompanied by altered energy generation and oxidative stress at retinal protein levels. The results in the retina were also compared to our previous study in vitreous using ICPL quantitative technology. We have now presented the protein changes in these two adjacent tissues, which may provide extra information of protein changes during ocular growth in myopia.

TSH/IGF1 receptor crosstalk: Mechanism and clinical implications

Increasing evidence of interdependence between G protein-coupled receptors and receptor tyrosine kinase signaling pathways has prompted reevaluation of crosstalk between these receptors in disease and therapy. Investigations into thyroid-stimulating hormone (TSH) and insulin-like growth factor 1 (IGF1) receptor crosstalk, and its application to the clinic have in particular shown recent progress. In this review, we summarize current insights into the mechanism of TSH/IGF1 receptor crosstalk. We discuss evidence that crosstalk is one of the underlying causes of TSHR-based disease and the feasibility of using combinations of TSH receptor and IGF1 receptor antagonists to increase the therapeutic index for the treatment of Graves' hyperthyroidism and Graves' ophthalmopathy.

Insulin-like growth factor-1 enhances the expression of functional TSH receptor in orbital fibroblasts from thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO), an autoimmune disease, occurs in approximately 50 % of patients with Graves' hyperthyroidism. Thyroid-stimulating hormone receptor (TSHR) that is expressed in orbital fibroblasts is the autoimmune target in the development of TAO. In addition to thyroid-stimulating immunoglobulin (TSI), insulin-like growth factor (IGF)-1 is also involved in the development of TAO. IGF-1 has been reported to potentiate the effects of thyroid-stimulating hormone (TSH) and TSI on TSHR signaling. In the current study, we investigated the effects of IGF-1 on the cell surface expression of the functional TSHR and its possible mechanism of action in human orbital fibroblasts. Our results show that orbital fibroblasts from the TAO patients expressed higher levels of IGF-1 receptor (IGF-R), compared to control subjects. Treatment with IGF-1 enhanced the expression of surface TSHR in orbital fibroblasts from TAO patients, but not from control subjects. In addition, treatment with IGF-1 increased the level of TSHR at both the protein and mRNA levels. Furthermore, pre-treatment with IGF-1 potentiated TSH-induced cAMP production, compared to cells that were treated with only TSH. Our results also show that pre-treatment with cycloheximide, an inhibitor of mRNA translation, partially, but not completely, inhibited the expression of TSHR on the cell surfaces of orbital fibroblasts from TAO patients. These collective results show that IGF-1enhances the cell surface expression of functional TSHR, not only by increasing TSHR expression, but also by inducing TSHR translocation to the plasma membrane in orbital fibroblasts from TAO.

Aggressive papillary thyroid carcinoma in a child with type 2 congenital generalized lipodystrophy

Thyroid carcinoma (TC) is rare in children, particularly in those aged < 10 years. Several studies have demonstrated a correlation between neoplasms and hyperinsulinemia and insulin resistance, which are often associated with a higher risk for and/or aggressiveness of the neoplasm. Congenital generalized lipodystrophy (CGL) with autosomal recessive inheritance is a rare disease and is characterized by the lack of adipose tissue, severe insulin resistance, and early metabolic disturbances. Here, we reported a rare case of a type 2 CGL in a girl who presented with a papillary TC (PTC) at the age of 7 years. She had no family history of TC or previous exposure to ionizing radiation. She had a generalized lack of subcutaneous fat, including the palmar and plantar regions, muscle hypertrophy, intense acanthosis nigricans, hepatomegaly, hypertriglyceridemia, severe insulin resistance, and hypoleptinemia. A genetic analysis revealed a mutation in the BSCL2 gene (p.Thr109Asnfs* 5). Ultrasound revealed a hypoechoic solid nodule measuring 1.8 × 1.0 × 1.0 cm, and fine needle aspiration biopsy suggested malignancy. Total thyroidectomy was performed, and a histopathological examination confirmed PTC with vascular invasion and parathyroid lymph node metastasis (pT3N1Mx stage). This is the first report to describe a case of differentiated TC in a child with CGL. Severe insulin resistance that is generally observed in patients with CGL early in life, especially in those with type 2 CGL, may be associated with this uncommon presentation of aggressive PTC during childhood.

Thyroid Stimulating Hormone (TSH)/Insulin-like Growth Factor 1 (IGF1) Receptor Cross-talk in Human Cells

Thyroid stimulating hormone and insulin-like growth factor 1 receptors (TSHRs and IGF1Rs, respectively) interact leading to additive or synergistic stimulation of cellular responses. Recent findings provide evidence that the interaction between TSHRs and IGF1Rs is similar to that described for other G protein-coupled receptors and receptor tyrosine kinases. These types of interactions occur at or proximal to the receptors and are designated "receptor cross-talk." Herein, we describe our studies in human thyrocytes, human retro-orbital fibroblasts from Graves' orbitopathy patients and a model cell line that support the concept of TSHR/IGF1R cross-talk. We also discuss how receptor cross-talk is involved in stimulation by a monoclonal TSHR-stimulating antibody and how targeting both receptors may lead to novel treatments of Graves' orbitopathy.

Regulatory aspects of the human hypothalamus-pituitary-thyroid axis

Thyroid hormones are essential for growth, differentiation and metabolism during prenatal and postnatal life. The hypothalamus-pituitary-thyroid (HPT)-axis is optimized for these actions. Knowledge of this hormonal axis is derived from decades of experiments in animals and man, and more recently from spontaneous mutations in man and constructed mutations in mice. This review examines the HPT-axis in relation to 24 h TSH profiles in men in various physiological and pathophysiological conditions, including obesity, age, longevity, and primary as well as central hypothyroidism. Hormone rhythms can be analyzed by quantitative methods, e.g. operator-independent deconvolution, approximate entropy and fitting the 24-h component by Cosinor analysis or related procedures. These approaches have identified some of the regulatory components in (patho)physiological conditions.

TSH/IGF-1 Receptor Cross-Talk Rapidly Activates Extracellular Signal-Regulated Kinases in Multiple Cell Types

We previously showed that thyrotropin (TSH)/insulinlike growth factor (IGF)-1 receptor cross-talk appears to be involved in Graves' orbitopathy (GO) pathogenesis and upregulation of thyroid-specific genes in human thyrocytes. In orbital fibroblasts from GO patients, coadministration of TSH and IGF-1 induces synergistic increases in hyaluronan secretion. In human thyrocytes, TSH plus IGF-1 synergistically increased expression of the sodium-iodide symporter that appeared to involve ERK1/2 activation. However, the details of ERK1/2 activation were not known, nor was whether ERK1/2 was involved in this synergism in other cell types. Using primary cultures of GO fibroblasts (GOFs) and human thyrocytes, as well as human embryonic kidney (HEK) 293 cells overexpressing TSH receptors (HEK-TSHRs), we show that simultaneous activation of TSHRs and IGF-1 receptors (IGF-1Rs) causes rapid, synergistic phosphorylation/activation of ERK1 and ERK2 in all three cell types. This effect is partially inhibited by pertussis toxin, an inhibitor of TSHR coupling to Gi/Go proteins. In support of a role for Gi/Go proteins in ERK1/2 phosphorylation, we found that knockdown of Gi(1-3) and Go in HEK-TSHRs inhibited ERK1/2 phosphorylation stimulated by TSH and TSH plus IGF-1. These data demonstrate that the synergistic effects of TSH plus IGF-1 occur early in the TSHR signaling cascade and further support the idea that TSHR/IGF-1R cross-talk is an important mechanism for regulation of human GOFs and thyrocytes.

Growth hormone and insulin-like growth factor 1 affect the severity of Graves' disease

Graves' disease, the most common form of hyperthyroidism in iodine-replete countries, is associated with the presence of immunoglobulins G (IgGs) that are responsible for thyroid growth and hyperfunction. In this article, we report the unusual case of a patient with acromegaly and a severe form of Graves' disease. Here, we address the issue concerning the role of growth hormone (GH) and insulin-like growth factor 1 (IGF1) in influencing thyroid function. Severity of Graves' disease is exacerbated by coexistent acromegaly and both activity indexes and symptoms and signs of Graves' disease improve after the surgical remission of acromegaly. We also discuss by which signaling pathways GH and IGF1 may play an integrating role in regulating the function of the immune system in Graves' disease and synergize the stimulatory activity of Graves' IgGs.

LEARNING POINTS

Clinical observations have demonstrated an increased prevalence of euthyroid and hyperthyroid goiters in patients with acromegaly.The coexistence of acromegaly and Graves' disease is a very unusual event, the prevalence being <1%.Previous in vitro studies have showed that IGF1 synergizes the TSH-induced thyroid cell growth-activating pathways independent of TSH/cAMP/PKA cascade.We report the first case of a severe form of Graves' disease associated with acromegaly and show that surgical remission of acromegaly leads to a better control of symptoms of Graves' disease.

Focus on GH deficiency and thyroid function

The relationships between GH system and hypothalamic-pituitary-thyroid axis are complex and not yet fully understood. The reported effects of GH administration on thyroid status of GHD patients have been remarkably divergent. This review will focus on the main studies aimed to clarify the effects of GH on thyroid function, firstly going through the diagnosis of central hypothyroidism and its possible pitfalls, then elucidating the possible contexts in which GHD may develop and examining the proposed mechanisms at the basis of interactions between the GH-IGF-I system and the hypothalamic-pituitary-thyroid axis.

Effects of GH replacement therapy on thyroid volume and nodule development in GH deficient adults: a retrospective cohort study

OBJECTIVE

Despite the well-known effects of GH/IGF1 signaling on the thyroid, few data are available on the risk of developing nodular goiter in hypopituitary subjects during GH replacement therapy (GHRT). We aimed to define the effects of GH therapy on thyroid volume (TV) and nodular growth.

DESIGN

The records of 96 subjects (47 males and 49 females, median age 48 years) with GH deficit (GHD) were investigated. Seventy also had central hypothyroidism (CH). At the time of our retrospective evaluation, median treatment duration was 5 years.

RESULTS

Pre-treatment TV was smaller in GHD patients than in healthy subjects (P=0.030). During GH treatment, TV significantly increased (P=0.016 for the entire group and P=0.014 in euthyroid GHD patients). Before starting GH therapy, 17 patients harbored thyroid nodules. During GH therapy, nodule size increased slightly in seven patients, and new thyroid nodules occurred in nine patients. Among the 79 patients without pre-existing thyroid nodules, 17 developed one or more nodules. There was no difference in the prevalence of CH in GHD patients with or without thyroid nodules (P=0.915; P=0.841, when patients with pre-therapy nodular goiter were excluded), the main predictor for nodule development being serum IGF1 (P=0.038).

CONCLUSIONS

GHRT is associated with TV's increase in GHD patients. Thyroid nodules developed in 27% of patients, mainly in relation to pre-therapy IGF1 levels, independently of normal or impaired TSH stimulation.

Obesity and thyroid cancer

Many studies have provided observational data on the association of obesity and thyroid cancers, but only few of them propose mechanisms that would permit a better understanding of the causal molecular mechanisms of this association. Considering that there is an increasing incidence of both obesity and thyroid cancers, we need to summarize and link recent studies in order to characterize and understand the contribution of obesity-related factors that might affect thyroid cancer development and progression. Adipose tissue is involved in many vital processes, including insulin sensitivity, angiogenesis, regulation of energy balance, activation of the complement system, and responses such as inflammation. Although these processes have their own molecular pathways, they involve the same molecules through which obesity and adipose tissue might exert their roles in carcinogenesis, not only affecting MAPK and PI3K or even insulin pathways, but also recruiting local inflammatory responses that could result in disease formation and progression. This review describes five important issues that might explain the link between excessive weight and thyroid cancer: thyroid hormones, insulin resistance, adipokines, inflammation, and sexual hormones.

Thyrotropin secretion in healthy subjects is robust and independent of age and gender, and only weakly dependent on body mass index

CONTEXT

Studies of the influence of sex, age, and body weight on TSH secretion are not unanimous. Most reports are based on a single TSH measurement; studies using frequent blood sampling are scarce and include a limited number of selected subjects.

OBJECTIVE

The goal was to investigate TSH dynamics in 117 healthy adults.

METHODS

TSH was measured by a sensitive immunofluorometric assay. Secretion parameters were quantified by automated deconvolution, approximate entropy [ApEn], spikiness, and diurnal properties.

RESULTS

Mean age was 43 years (range, 22-77 y). Mean body mass index (BMI) was 26.8 kg/m(2) (range, 18.3-39.4 kg/m(2)). Daily TSH secretion was 45.4 mU/L (range, 8.0-207 mU/L). There were no sex differences in secretion parameters, including pulse frequency; basal, pulsatile, and total secretion; pulse mode; half life; pulse regularity; ApEn; spikiness; and nycthemeral properties. BMI was positively related to basal secretion. Total secretion correlated negatively with free T₄ (R = 0.225; P = .018). The onset of the nocturnal surge was delayed by increasing BMI and advanced by increasing age. ApEn and spikiness correlated positively with age, especially in men. The 9 am sample correlated strongly with the total 24-hour secretion, explaining two-thirds of the variability.

CONCLUSION

This study shows that the 24-hour TSH secretion in healthy volunteers is stable and robust and not influenced by sex, BMI, and age. ApEn in the elderly, especially men, is increased, pointing to a less tight feedback control. Furthermore, aging is associated with advance shifting of the TSH rhythm, which is a phenomenon also observed in other biological rhythms.

Thyrotropin secretion patterns in health and disease

Thyroid hormones are extremely important for metabolism, development, and growth during the lifetime. The hypothalamo-pituitary-thyroid axis is precisely regulated for these purposes. Much of our knowledge of this hormonal axis is derived from experiments in animals and mutations in man. This review examines the hypothalamo-pituitary-thyroid axis particularly in relation to the regulated 24-hour serum TSH concentration profiles in physiological and pathophysiological conditions, including obesity, primary hypothyroidism, pituitary diseases, psychiatric disorders, and selected neurological diseases. Diurnal TSH rhythms can be analyzed with novel and precise techniques, eg, operator-independent deconvolution and approximate entropy. These approaches provide indirect insight in the regulatory components in pathophysiological conditions.

IGF-1 receptor deficiency in thyrocytes impairs thyroid hormone secretion and completely inhibits TSH-stimulated goiter

Although thyroid-stimulating hormone (TSH) is known to be a major regulator of thyroid hormone biosynthesis and thyroid growth, insulin-like growth factor 1 (IGF-1) is required for mediating thyrocyte growth in concert with TSH in vitro. We generated mice with thyrocyte-selective ablation of IGF-1 receptor (TIGF1RKO) to explore the role of IGF-1 receptor signaling on thyroid function and growth. In 5-wk-old TIGF1RKO mice, serum thyroxine (T4) concentrations were decreased by 30% in concert with a 43% down-regulation of the monocarboxylate transporter 8 (MCT8), which is involved in T4 secretion. Despite a 3.5-fold increase in circulating concentrations of TSH, thyroid architecture and size were normal. Furthermore, thyrocyte area was increased by 40% in WT thyroids after 10 d TSH injection, but this effect was absent in TSH-injected TIGF1RKO mice. WT mice treated with methimazole and sodium perchlorate for 2 or 6 wk exhibited pronounced goiter development (2.0 and 5.4-fold, respectively), but in TIGF1RKO mice, goiter development was completely abrogated. These data reveal an essential role for IGF-1 receptor signaling in the regulation of thyroid function and TSH-stimulated goitrogenesis.

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 (125)I 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 (125)I 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.

Effects of depot growth hormone replacement on thyroid function and volume in adults with congenital isolated growth hormone deficiency

BACKGROUND

Conflicting data exist on the effects of GH replacement therapy (GHRT) on thyroid function and thyroid volume (TV) in GH-deficient (GHD) patients.

AIM

The aim of this study was to assess the effects of GHRT on thyroid function and TV in adults with congenital lifetime isolated GHD (IGHD).

SUBJECTS AND METHODS

We studied 20 GH-naïve adults with IGHD due to a homozygous mutation of the GHRH-receptor gene at baseline, after 6-month depot- GH replacement therapy (pGH), and 6-month washout (6mo). Total T(3), free T(4) (FT(4)), reverse T(3) (rT(3)), TSH, IGF-I, SHBG, and TV were measured; body surface area-corrected TV (CTV) was calculated.

RESULTS

IGF-I and T(3) increased pGH. T(3) levels remained elevated at 6mo. GHRT did not significantly change FT(4), rT(3), TSH, and SHBG. TV and CTV increased pGH and remained elevated at 6mo.

CONCLUSIONS

GHRT in IGHD adults caused an increase in serum T(3) levels and TV, suggesting an important role of the GH-IGF-I axis in thyroid function.

TSH compensates thyroid-specific IGF-I receptor knockout and causes papillary thyroid hyperplasia

Although TSH stimulates all aspects of thyroid physiology IGF-I signaling through a tyrosine kinase-containing transmembrane receptor exhibits a permissive impact on TSH action. To better understand the importance of the IGF-I receptor in the thyroid in vivo, we inactivated the Igf1r with a Tg promoter-driven Cre-lox system in mice. We studied male and female mice with thyroidal wild-type, Igf1r(+/-), and Igf1r(-/-) genotypes. Targeted Igf1r inactivation did transiently reduce thyroid hormone levels and significantly increased TSH levels in both heterozygous and homozygous mice without affecting thyroid weight. Histological analysis of thyroid tissue with Igf1r inactivation revealed hyperplasia and heterogeneous follicle structure. From 4 months of age, we detected papillary thyroid architecture in heterozygous and homozygous mice. We also noted increased body weight of male mice with a homozygous thyroidal null mutation in the Igf1r locus, compared with wild-type mice, respectively. A decrease of mRNA and protein for thyroid peroxidase and increased mRNA and protein for IGF-II receptor but no significant mRNA changes for the insulin receptor, the TSH receptor, and the sodium-iodide-symporter in both Igf1r(+/-) and Igf1r(-/-) mice were detected. Our results suggest that the strong increase of TSH benefits papillary thyroid hyperplasia and completely compensates the loss of IGF-I receptor signaling at the level of thyroid hormones without significant increase in thyroid weight. This could indicate that the IGF-I receptor signaling is less essential for thyroid hormone synthesis but maintains homeostasis and normal thyroid morphogenesis.

Serum thyrotropin as a risk factor for thyroid malignancy in euthyroid subjects with thyroid micronodule

BACKGROUND

An elevated thyroid stimulating hormone (TSH) level is a risk factor for differentiated thyroid cancer. The present study investigated whether TSH is a risk factor for thyroid microcarcinoma (TMC) in euthyroid subjects with a micronodule.

METHODS

In this cross-sectional study, 483 euthyroid subjects (77 males patients, 406 females patients) with a thyroid micronodule were enrolled and underwent ultrasound guided fine-needle aspiration biopsy. Serum TSH level was measured in every subject. The final diagnostic outcome (malignant or benign) was defined in conjunction with cytology and histology.

RESULTS

Compared with the patients below the population mean, patients above the population mean had a significantly higher malignancy rate (10.8% vs 4.8%, p = .025). Multiple logistic regression analysis revealed TSH as an independent risk factor for malignancy in euthyroid patients with a micronodule (odds ratio, 1.449; 95% confidence interval, 1.033-2.033; p = .031).

CONCLUSIONS

Measurement of TSH in subjects with a thyroid micronodule is helpful to estimate cancer risk.

Molecular pathogenesis of nodular goiter

INTRODUCTION

Familial clustering of goiters mostly with an autosomal dominant pattern of inheritance has repeatedly been reported. Moreover, other environmental and etiologic factors are likely to be involved in the development of euthyroid goiter. Therefore, a multifactorial etiology based on complex interactions of both genetic predisposition and the individuals' environment is likely.

METHODS

The line of events from early thyroid hyperplasia to multinodular goiter argues for the predominant neoplastic (i.e., originating from a single mutated cell) character of nodular structures. Etiologically, relevant somatic mutations are known in two thirds of papillary and follicular thyroid carcinomas and hot thyroid nodules. In contrast, the somatic mutations relevant for benign cold or benign isocaptant thyroid nodules which constitute the majority of thyroid nodules are unknown.

RESULTS

The nodular process is triggered by the oxidative nature of thyroid hormone synthesis or additional oxidative stress caused by iodine deficiency or smoking. If the antioxidant defense is not effective, this oxidative stress will cause DNA damage followed by an increase of the spontaneous mutation rate which is a substrate for tumorogenesis.

CONCLUSIONS

Therefore, the hallmark of thyroid physiology--H(2)O(2) production during hormone synthesis--is very likely the ultimate cause for the frequent mutagenesis in the thyroid gland. Because iodine deficiency increases the oxidative burden, DNA damage and mutagenesis could provide the basis for the frequent nodular transformation of endemic goiters.

Conditional deletion of insulin receptor in thyrocytes does not affect thyroid structure and function

Thyroid-stimulating hormone (TSH) is the primary regulator of thyroid growth and function acting via cyclic AMP signaling cascades. In cultured thyrocytes, insulin and/or insulin-like growth factor-1 (IGF-1) are required for mediating thyrocyte proliferation in concert with TSH. To determine the role of insulin signaling in thyroid, growth in vivo, mice with thyrocyte-selective ablation of the insulin receptor (IR) were generated by crossing mice homozygous for a floxed IR allele with transgenic mice in which thyrocyte-specific expression of Cre recombinase was driven by the human thyroid peroxidase (TPO) gene promoter. Immunohistochemistry and Western blot analysis confirmed near complete loss of IR expression in the thyroid of thyrocyte IR knockout mice. These mice are viable and have no obvious thyroid dysfunction and macro- and microscopic thyroid morphology was normal. Thus, insulin signaling in thyrocytes does not play an essential role in the architecture and function of the thyroid in vivo.

Molecular regulation of thyroid gland function

PURPOSE OF REVIEW

For de-novo thyroid hormone synthesis ex vivo, thyroid follicular cells require a serum-free medium supplying nutrients, iodide, thyroid-stimulating hormone and insulin-like growth factor I (IGF-I) (or insulin). Under these conditions, T3 and T4 are secreted but so are other factors such as growth factors, plasminogen activators, their inhibitors known as serpins, and so on. What is the function of these factors? Do thyroid cells respond to them or are these paracrine/endocrine factors? The purpose of this review is to highlight the current developments in the identification and role of the signalling pathways that regulate thyroid growth and function and the putative role of endogenous thyroid proteases in regulating this.

RECENT FINDINGS

The roles of the mitogen-activated protein kinases and phosphoinositol 3 kinases and integrins in mediating growth and function in thyroid cancer cells and the roles of plasminogen activators, their receptors and the downstream signalling pathways they modulate have been developed. Discoveries of novel proteases, expressed in thyroid cancers, may be useful in diagnosis.

SUMMARY

The signalling pathways regulating thyroid activity are examined and the roles of follicular cell products in maintaining thyroid homeostasis evaluated. The possibility that thyroid cell products other than T3 and T4 may circulate and have extrathyroidal effects is proposed.

Biochemical changes during goiter induction by methylmercaptoimidazol and inhibition by delta-iodolactone in rat

BACKGROUND

We have demonstrated that the administration of delta-iodolactone (i.e., 5-iodo-delta lactone) of arachidonic acid (IL-delta), a mediator in thyroid autoregulation, prevents goiter induction by methylmercaptoimidazol (MMI) in rats. Other studies have shown that transforming growth factor beta-1 (TGF-beta1) mimics some of the actions of excess iodide, but its participation in autoregulation is disputed. The present studies were performed to test the hypotheses that IL-delta decreases thyroid growth by inhibition of cell proliferation and/or by stimulation of apoptosis due to oxidative stress, that TGF-beta is stimulated by an excess of iodide and by IL-delta, and that c-Myc and c-Fos expression are upregulated during goiter induction and downregulated during goiter inhibition.

METHODS

Rats were treated with MMI alone or together with iodide or IL-delta. Thyroid weight, cell number, cell proliferation, apoptosis, and oxidative stress were determined. Proliferating cell nuclear antigen (PCNA), TGF-beta1, TGF-beta3, c-Myc, and c-Fos were measured by Western blot.

RESULTS

MMI caused a progressive increase in thyroid weight accompanied by an increase in cell number, asymmetry of the ploidy histograms, and PCNA, c-Fos, and c-Myc expression. In addition, an early increase of apoptosis was observed. Peroxides as well as glutathione peroxidase and catalase activities were also increased in goitrous animals. The inhibitory action of IL-delta on goiter formation was accompanied by the inhibition of cell proliferation evidenced by a significant decrease in cell number, PCNA expression, and asymmetry of the ploidy histograms. A transient stimulation of apoptosis after 7 days of treatment was also observed. MMI administration stimulated TGF-beta1 but not TGF-beta3 synthesis. IL-delta alone caused a slight increase of TGF-beta3 but not TGF-beta1, whereas potassium iodide (KI) stimulated both isoforms and MMI reversed KI effect on TGF-beta1 expression but not on TGF-beta3.

CONCLUSIONS

The goiter inhibitory action of IL-delta is due to the inhibition of cell proliferation and the transient stimulation of apoptosis. This latter action does not involve oxidative stress. TGF-beta1 does not play a role in the autoregulatory pathway mediated by IL-delta. Iodide stimulates TGF-beta3 without the need of being organified. These results suggest that there may be more than one pathway involved in the autoregulatory mechanism.

Association of thyroid gland volume, serum insulin-like growth factor-I, and anthropometric variables in euthyroid prepubertal children

CONTEXT AND OBJECTIVE

Few studies have focused on the interrelation between thyroid size, anthropometric variables, and IGF-I in adults, but such data are lacking for children. We have investigated thyroid gland volume and several hormonal and anthropometric variables in prepubertal children.

DESIGN AND PARTICIPANTS

A total of 859 prepubertal euthyroid Danish children aged 4-9 yr underwent a thorough clinical investigation, including anthropometrical measurements and determination of TSH, thyroid hormones, autoantibodies, urinary iodine excretion, and thyroid volume (TV) by ultrasound. Longitudinal growth data from birth were available.

RESULTS

TV increased significantly with age (r = 0.487; P < 0.001). Mean TV +/- sd for different age groups were as follows: 4 yr, 2.2 +/- 1.4 ml; 5 yr, 2.5 +/- 1.3 ml; 6 yr, 2.8 +/- 1.3 ml; 7 yr, 3.2 +/- 1.3 ml; 8 yr, 3.5 +/- 1.3 ml; 9 yr, 3.7 +/- 1.3 ml. We found a significant positive association between IGF-I and TV (P < 0.001). Furthermore, in multiple regression analyses, TSH (P < 0.013), free T(4) (P < 0.001), lean body mass (P < 0.001), and body surface area (P < 0.001) as well as other anthropometrical measurements were identified as factors significantly associated with TV. Family history of thyroid disease and presence of incidental abnormal ultrasound findings were also positively associated with TV (P = 0.025 and 0.022, respectively).

CONCLUSIONS

In our cohort of prepubertal Danish children, the GH/IGF-I-axis was positively correlated with thyroid size, suggesting a role in the regulation of thyroid growth. Moreover, anthropometric measurements, in particular body surface area, were the best predictors of TV.

Levothyroxine therapy in preventing nodular recurrence after hemithyroidectomy: a retrospective study

AIM

To determine the effect of levothyroxine (L-T4) therapy on the recurrence rate of nodular disease in patients previously treated with lobectomy for benign nodular goiter.

METHODS

Two hundred and thirty-tree patients (38 males, 195 females; age 49.9+/-13.1 yr) with no post-surgical evidence of nodular disease in the remnant, were followed- up yearly with serum TSH and ultrasound (US). Nodular recurrence was defined as a lesion of at least 5 mm at US. Patients were divided in 2 groups based on whether or not they had been treated with L-T4 after surgery: Group 1 (45 patients) who did not receive any L-T4, and Group 2 (188 patients) treated with L-T4. Group 2 was further subdivided in Group 2a (123 patients) receiving L-T4 substitutive therapy (TSH>or=0.5 and <or=3 mUI/l) and Group 2b (65 patients) receiving L-T4 at TSH-suppressive dose (TSH<0.5 mUI/l).

RESULTS

Mean observation period was 5.8+/-4.7 yr. Overall, 71 out of 233 (30.5%) patients experienced recurrence of thyroid nodular disease: 29 patients (64.4%) in Group 1, 24 (19.5%) patients in Group 2a, and 18 (27.7%) patients in Group 2b. The recurrence rate was significantly lower (p<0.001) in Group 2 compared with Group 1, but no significant difference was observed between Groups 2a and 2b.

CONCLUSION

In patients who have undergone hemithyroidectomy for benign monolobar nodular disease, L-T4 therapy may prevent recurrence of nodular disease. TSH suppression may not be required for prevention of recurrence in the remnant thyroid tissue.

Regulation of plasminogen activators in human thyroid follicular cells and their relationship to differentiated function

Human thyroid cells in culture take up and organify (125)I when cultured in TSH (acting through cAMP) and insulin. They also secrete urokinase (uPA) and tissue-type (tPA) plasminogen activators (5-100 IU/10(6)cells/day). TSH and insulin both decreased secreted PA activity (PAA), uPA and tPA protein and their mRNAs. Autocrine fibroblast growth factor increased secreted PAA and inhibited thyroid cell (125)I uptake. Epidermal growth factor (EGF) and the protein kinase C (PKC) activator, TPA significantly increased PAA and inhibited thyroid differentiated function, (TPA > EGF). For TPA, effects were rapid, increased PAA secretion and decreased (125)I uptake being seen at 4 h whereas for EGF, a 24 h incubation was required. qRT-PCR showed significantly increased mRNA expression of uPA with lesser effects on tPA. Aprotinin, which inhibits PAA, increased (125)I uptake but did not abrogate the effects of TPA and EGF. The MEKK inhibitor, PD98059 partially reversed the effects of EGF and TPA on PAA, and largely reversed the effects of EGF but not TPA on differentiated function. PKC inhibitors bisindoylmaleimide 1, and the specific PKCbeta inhibitor, LY379196 completely reversed the effects of TPA on (125)I uptake and PAA whereas EGF effects were unaffected. TPA inhibited follicle formation and this effect was blocked by LY379196 but not PD98059. We conclude that in thyroid cells, MAPK activation inversely correlates with (125)I uptake and directly correlates with PA expression, in contrast to the effects of cAMP. TPA effects on iodide metabolism, dissolution of follicles and uPA synthesis are mediated predominantly through PKCbeta whereas EGF exerts its effects through MAPK but not PKCbeta.

Thyroid morphology and function in adults with untreated isolated growth hormone deficiency

OBJECTIVE

GH influences thyroid function and anatomy. Although goiter is frequent in acromegalic patients, the effects of GH deficiency (GHD) are difficult to assess, because hypopituitaric subjects who lack GH often also have a partial or complete deficit of TSH.

STUDY DESIGN

We studied thyroid morphology and serum levels of thyroid hormones in adult members of a large Brazilian kindred with untreated isolated GHD due to a homozygous mutation in the GHRH receptor gene (GHRHR; nine men and 15 women; GHD group) and compared them to subjects heterozygous for the same mutation (eight men and 10 women; HET group) and subjects homozygous for the wild-type allele [seven men and 11 women; control (CO) group].

RESULTS

GHD subjects had a smaller thyroid volume (TV) than HET and CO. The TV of the HET group was intermediate between those of the GHD and CO groups. When TV was corrected by body surface area, it remained smaller in the GHD and HET groups than in the CO group, but the difference between GHD and HET groups disappeared. The GHD group had lower serum T3 levels than the CO group and higher free T4 levels than HET and CO groups.

CONCLUSIONS

Individuals with severe untreated GHD due to a homozygous GHRHR mutation and heterozygous carriers of the same mutation have smaller TV than normal subjects, suggesting that GH has a permissive role in the growth of the thyroid gland. In addition, GHD subjects have reduced serum total T3 and increased serum free T4, suggesting a reduction in the function of the deiodinase system.

Molecular pathogenesis of euthyroid and toxic multinodular goiter

The purpose of this review is to summarize current knowledge of the etiology of euthyroid and toxic multinodular goiter (MNG) with respect to the epidemiology, clinical characteristics, and molecular pathology. In reconstructing the line of events from early thyroid hyperplasia to MNG we will argue the predominant neoplastic character of nodular structures, the nature of known somatic mutations, and the importance of mutagenesis. Furthermore, we outline direct and indirect consequences of these somatic mutations for thyroid pathophysiology and summarize information concerning a possible genetic background of euthyroid goiter. Finally, we discuss uncertainties and open questions in differential diagnosis and therapy of euthyroid and toxic MNG.

Expression of insulin-like growth factor I (IGF-I) gene and of genes for IGF-binding proteins 1, 2, 3, 4 (IGFBP-1-IGFBP-4) in non-neoplastic human thyroid cells and in certain human thyroid cancers. Effect of exogenous IGF-I on this expression

AIM

The aim of this study was to examine the expression of the IGF-I gene and of genes for IGFBP-1, -2, -3, and -4 in cells from nodular goiters (NG), and from different human thyroid carcinomas (papillary--PTC, anaplastic--ATC, and medullary--MTC), cultured in monolayers. The influence, exerted by exogenous IGF-I on the expression of these genes, was also investigated.

METHODS

Thyroid tissue specimens were obtained from 65 patients during subtotal or total thyroidectomies. After approximately 2-3 weeks of culture, thyroid cells were incubated for 24 hours with IGF-I in concentrations of: 0, 1, 10 and 100 ng/ml. The total mRNA was isolated according to the method described by Chomczyński and Sacchi with our own modifications. Afterwards, mRNA encoding IGF-I, IGFBP-1-IGFBP-4 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were amplified, using the reverse transcription-polymerase chain reaction (RT-PCR); GAPDH gene served as a control gene. PCR products were electrophoresed and then submitted to densitometric analysis.

RESULTS AND CONCLUSIONS

Our study has shown that in carcinoma cells (ATC, PTC, MTC), IGF-I reveals a stimulatory influence on the expression of its own gene, that effect being most distinctive in ATC cells. These facts indicate an important role of IGF-I in the pathogenesis and invasiveness of the analyzed malignant neoplasms.

Local factors regulating growth and function of human thyroid cells in vitro and in vivo

In vitro culture of thyroid follicles is often employed to study thyroid cell biology and the control of thyroid follicular cell growth. For acceptance as a valid model, cultures should maintain differentiated function, which can be measured as the organification of [Formula: see text] and/or the de novo synthesis of thyroid hormones. In this article, the properties and merits of the various in vitro cultures of thyroid follicular cells and the potential effects of thyroid-specific, secreted products (thyroid hormones, thyroglobulin) and autocrine factors (proteases, growth factors and inhibitors) on thyroid growth and function, are explored. The regulation of the secretion of autocrine/paracrine factors by thyroid follicular cells is reviewed and methods by which cells may defend themselves from the effects of bioactive growth factors are discussed with particular reference to FGF signalling. The role and regulation of plasminogen activator activity, which may be central to the release and/or activation of growth factors and their receptors, and the secretion of angiogenic factors are described.

Isolation of a normal human thyroid cell line: hormonal requirement for thyroglobulin regulation

The long-term culture of functional follicular cells from normal adult human thyroid tissue has been obtained. They were expanded using a 1:2 split ratio until passage 28 (present status) in Click-RPMI medium enhanced with 5% fetal calf serum and diverse associations of hormones or components including porcine insulin and bovine thyrotropin. At passages 10 and 20, chromosome countings showed a normal diploid number and a normal karyotype. In calf serum containing media, cells are epithelial in the presence of thyrotropin (TSH) but present a slight elongated form in the absence of TSH. In serum-free media, 30 minutes after TSH stimulation, both epithelial and elongated cells changed in morphology to stellate-shaped, arborized forms, indicating the presence of functional TSH-receptors even in long term (18 months) TSH-free cultures. Cells produce thyroglobulin constitutively and large amounts of thyroglobulin are easily recovered in TSH-supplemented media, especially in the presence of insulin. Thyroglobulin production was increased versus days under TSH or insulin stimulation. Combination of the two hormones clearly resulted in a synergistic and not an additive effect. The other hormones present in the 6H components (transferrin, glycylhistidyl-lysine, somatostatin, and hydrocortisone) had no positive effect on thyroglobulin accumulation in media in our experimental conditions. Addition of TSH to hormone-free cultures or to insulin-, insulin plus hydrocortisone-, or 5H-containing cultures resulted in a clear increase in thyroglobulin production. Withdrawal of TSH from 6H cultures resulted in a decrease in thyroglobulin accumulation in media. Six months were required to select fibroblast-free cultures and to get passage 6. But only 17 months separated passage 6 to passage 28, indicating that the proliferative rate is increasing with in vitro cell adaptation. Such normal adult thyroid cells, thyroglobulin-producing, TSH, and insulin-sensitive, represent a new normal human thyroid cell line allowing comparative studies with cells originating from pathologic thyroid tissues.

Regulation of thyroid cell proliferation by TSH and other factors: a critical evaluation of in vitro models

TSH via cAMP, and various growth factors, in cooperation with insulin or IGF-I stimulate cell cycle progression and proliferation in various thyrocyte culture systems, including rat thyroid cell lines (FRTL-5, WRT, PC Cl3) and primary cultures of rat, dog, sheep and human thyroid. The available data on cell signaling cascades, cell cycle kinetics, and cell cycle-regulatory proteins are thoroughly and critically reviewed in these experimental systems. In most FRTL-5 cells, TSH (cAMP) merely acts as a priming/competence factor amplifying PI3K and MAPK pathway activation and DNA synthesis elicited by insulin/IGF-I. In WRT cells, TSH and insulin/IGF-I can independently activate Ras and PI3K pathways and DNA synthesis. In dog thyroid primary cultures, TSH (cAMP) does not activate Ras and PI3K, and cAMP must be continuously elevated by TSH to directly control the progression through G(1) phase. This effect is exerted, at least in part, via the cAMP-dependent activation of the required cyclin D3, itself synthesized in response to insulin/IGF-I. This and other discrepancies show that the mechanistic logics of cell cycle stimulation by cAMP profoundly diverge in these different in vitro models of the same cell. Therefore, although these different thyrocyte systems constitute interesting models of the wide diversity of possible mechanisms of cAMP-dependent proliferation in various cell types, extrapolation of in vitro mechanistic data to TSH-dependent goitrogenesis in man can only be accepted in the cases where independent validation is provided.

Testosterone and estradiol modulate TSH-binding in the thyrocytes of Wistar rats: influence of age and sex

Age and sex are important factors that influence thyroid pathophysiology. Though sex steroids are known to enhance thyrotropin (TSH) mRNA expression and incidence of thyroid tumours, there is no report on their effects on TSH action under normal physiological conditions. In the present study, the effects of testosterone (T) and estradiol (E2) on thyroidal TSH-receptor (TSH-R) concentration, and TSH-binding to thyrocytes (in vitro) were elucidated in immature and mature Wistar rats. Immature (10 days old) and adult (120 days old) rats of either sex were gonadectomized (GDX) and one group of GDX rats was treated with physiological doses of T and another with E2. Immature GDX rats were supplemented with the steroids for 10 days and adults were supplemented with the steroids for 30 days. While supplementation of steroids to immature rats was begun immediately after surgery, for adult rats it was started 10 days after gonadectomy. The rats were killed at the end of the experimental period. Gonadectomy significantly decreased serum TSH, and TSH-R concentration under in vivo condition and [125I]-TSH binding to thyrocytes under in vitro conditions. Supplementation of T to male and E2 to female GDX rats restored normality of the parameters. Thyrocytes of immature male rats challenged with linearly increasing doses of TSH or T (6.25-800 ng/ml) showed a dose-dependent increase in TSH-binding. However, thyrocytes of immature female rats challenged with T showed a gender-specific response. While there was a linear increase in TSH-binding in thyrocytes of males, a biphasic response was evident in thyrocytes of females. In the case of thyrocytes from adult rats, T induced a dose-dependent change in TSH-binding in males, which reached the peak in response to 12.5 ng T, and diminished thereafter. In contrast, E2 was inhibitory to TSH-binding to thyrocytes of adult male rats. On the other hand, E2 showed a clear gender-specific stimulation of TSH-binding in thyrocytes of females and an inhibition of the same in males. TSH and sex steroids upregulated TSH receptors in immature rats, whereas the effect was biphasic in adult rat thyrocytes. It is concluded from the present study that sex steroids modulate TSH-binding in rat thyrocytes, which may vary according to the age and sex of the animals.

Insulin-like growth factor 1 expression in thyroid tumors

Insulin-like growth factor 1 (IGF-1) likely is involved in thyrocyte proliferation via autocrine mechanisms, but limited data are available on its in vivo expression in thyroid neoplasms. This prompted us to explore IGF-1 expression at the protein and mRNA levels and IGF-1 receptor (IGF-1rec) immunoreactivity in normal and neoplastic thyroids (50 adenomas and 53 carcinomas). We documented increased IGF-1 and IGF-1rec immunoreactivity in adenomas (31 of 50 and 40 of 50 cases, respectively) and carcinomas (38 of 53 and 42 of 53 cases) compared with normal thyroid, which only showed minimal immunoreactivity for the ligand and its receptor. A corresponding up-regulation of IGF-1 mRNA was documented in carcinomas, whereas adenomas exhibited down-regulated expression of IGF-1 mRNA. Immunoreactivity for IGF-1 and cognate receptor positively correlated with tumor diameter and wide intrathyroidal extension but not with patients' gender and age or with the stage of the tumors and the occurrence of lymph node metastases. These data emphasize a possible role of the IGF-1 system in thyroid tumorigenesis, as indicated by in vitro studies. In addition, the evaluation of IGF-1 and IGF-1rec immunoreactivity might have clinical implications, because it positively correlates with the aggressiveness of these tumors.

Effect of the interaction of TSH and insulin on the stimulation of 2-deoxyglucose uptake in FRTL-5 cells

Since thyroid glycogen stores are low, the uptake of glucose is very important in order to maintain cell function (house-keeping). Previous studies have shown that TSH and insulin, independently, are regulators of this parameter. Since their corresponding mechanisms of action are different, we investigated the possible effect of the interaction between TSH and insulin on the stimulation of 2-deoxyglucose (2-DOG) uptake, a non metabolizable derivative of glucose. Confluent FRTL-5 cells were submitted to different treatments, usually for 72 h. In one series of experiments the concentration of TSH was kept constant, at 1 U/l, and the addition of insulin, from 0.16 to 1.6 micromol/l caused a progressive synergic increase in DOG uptake. When insulin concentration was kept constant, increasing amounts of TSH, from 0.5 to 10 U/l), also caused a synergic stimulation of DOG uptake. The effect of insulin was mimicked by IGF-1 (1-10 nmol/l), while that of TSH was mimicked by forskolin. Timecourse studies showed that TSH had a peak at 3 h of incubation, while insulin caused a progressive increase for up to 72 h. At short incubation times, up to 6 h, an additive effect of TSH and insulin was observed, while at longer times the interaction was synergic. The present results suggest that the interaction between the cAMP and the tyrosine kinase pathways on DOG uptake would involve two different mechanisms. At early times the effects of both hormones are additive, while in longer periods it becomes synergic.

Somatostatin inhibits PC Cl3 thyroid cell proliferation through the modulation of phosphotyrosine activity. Impairment of the somatostatinergic effects by stable expression of E1A viral oncogene

In this study, we report the effects of somatostatin on the proliferation of PC C13 thyroid cell line and the intracellular mechanisms involved. We also evaluated the possible alterations, induced by E1A oncogene transformation on the intracellular pathways mediating somatostatin inhibition of cell proliferation. We showed that somatostatin was able to powerfully inhibit insulin- and insulin + TSH-dependent cell proliferation by inducing a block in the G1/S progression in the cell cycle. These cytostatic effects were completely reverted by vanadate, suggesting that somatostatin may induce antiproliferative effects through the modulation of phosphotyrosine phosphatases. In the E1A-transformed cell line, somatostatin was completely ineffective. The lack of somatostatin inhibitory effects on cell proliferation were not due to alterations in the expression of somatostatin receptors, which were regularly expressed and coupled to adenylyl cyclase activity, but were dependent on an alteration in their coupling with the phosphotyrosine phosphatase. In fact, although in PC C13 cells somatostatin increased by 100% phosphotyrosine phosphatase activity, it was completely ineffective in E1A-expressing cells. In conclusion we demonstrated that somatostatin activates phosphotyrosine phosphatases in PC C13 thyroid cells to inhibit cell proliferation and that the stable expression of E1A oncogene in these cells completely abolishes this antiproliferative effect.

Function of the homeo and paired domain proteins TTF-1 and Pax-8 in thyroid cell proliferation

The thyroid transcription factors TTF-1 and Pax-8 are homeobox- and paired box-containing genes, respectively, that are responsible for thyroid-specific gene expression, thyroid development, and thyroid cell differentiation. However, it is not clear if such factors play a role in thyroid cell proliferation. The antisense oligonucleotide strategy was used in order to clarify this point. Treatment of quiescent FRTL-5 thyroid cells with TTF-1 or Pax-8 antisense oligonucleotides caused a significant reduction in thyroid-stimulating hormone and insulin-like growth factor-I-stimulated cell proliferation, measured by DNA synthesis and cell counting. The same results were obtained with forskolin indicating that the TTF-1 or Pax-8 role in mediating the thyroid-stimulating hormone growth effect occurred via the cAMP pathway. The effect was higher with TTF-1 as the blockage by this factor caused a 65% decrease in cell proliferation compared to the control. Pax-8 blocking lead only to a 30% decrease. The blocking of both thyroid transcription factors together did not result in an additive effect. These data provide direct evidence that both homeo and paired box gene expression is essential for FRTL-5 thyroid cell proliferation, with each one possibly playing a different regulatory role.

Regulation of myo-inositol transport during the growth and differentiation of thyrocytes: a link with thyroid-stimulating hormone-induced phospholipase A2 activity

The Vmax of myo-inositol transport increased 3-fold during epidermal growth factor (EGF)-induced growth and thyroid-stimulating hormone. (TSH)-induced differentiation in primary cultures of sheep and human thyrocytes. The Km remained unaltered. This up-regulation required the presence of insulin. The TSH-induced rise in myo-inositol transport commenced 8 to 16 h after the initial stimulus and achieved a plateau at 24 h. In human thyrocytes the change in Vmax was accompanied by an increase in the steady-state levels of mRNA for the myo-inositol transporter following treatment with either ligand. Examination of the metabolites of myo-inositol showed few significant changes after treatment of sheep thyrocytes with EGF for 24 h. This is consistent with maintenance of the intracellular concentration of myo-inositol as the cells enlarge in preparation for cell division. In TSH-treated cells, however, up-regulation of myo-inositol transport was linked with increased myo-inositol cycling across the cell membrane, increased phospholipase A2-mediated turnover of phosphatidylinositol and a concomitant increase in arachidonic acid turnover. Increased levels of myo-inositol phosphates were also noted 24 h after TSH treatment. These results indicate the initiation of secondary signalling events many hours after the primary stimulus.

Biphasic effects of thyrotropin on invasion and growth of papillary and follicular thyroid cancer in vitro

The rationale for TSH suppression in the treatment of follicular thyroid cancer (FTC) and papillary thyroid cancer (PTC) is to inhibit tumor growth, prevent recurrent disease, and eventually prolong survival. We analyzed the effects of TSH on invasion and growth of 3 FTC cell lines from 1 patient (FTC133, primary; FTC236, lymph node; FTC238, lung metastasis) and 2 PTC cell lines (PTC-UC1, PTC-UC3). Cell growth and invasion through an 8-micron pore polycarbonate membrane coated with Matrigel were measured using the MTT assay. The dose-response to TSH was biphasic, stimulating invasion and growth of FTC and PTC at low concentrations (0.1-10 mU/mL), and inhibiting them at high concentrations (100 mU/mL). Interestingly, the metastatic FTC cell lines had higher basal invasion, but were less responsive to TSH than the primary tumor. TSH (1 mU/mL) stimulated invasion of FTC133 by 21%, FTC236 by 8%, and FTC238 by 8% (p < 0.01). At 100 mU/mL, TSH inhibited invasion of FTC133 by 21%, compared to 11% in FTC236 and 12% in FTC238. Also, TSH dose-dependently influenced proliferation of follicular thyroid cancer cells. At low concentrations it stimulated growth of FTC133 (20%) and inhibited it at high concentrations (23%; p < 0.01). Again, the amplitude of TSH effects was significantly smaller in the cell lines from metastatic tumors. TSH affected invasion and growth of PTC-UC1 and PTC-UC3 also biphasically. These results show that TSH may act as a mitogenic and antimitogenic growth factor for invasion and proliferation of well-differentiated thyroid cancer cells in vitro.

Insulin-like growth factor 1 (IGF-1) in multinodular goiters: a possible pathogenetic factor

In order to support previous in vitro studies which had stressed a possible autocrine role for Insulin-like Growth Factor 1 (IGF-1) in thyroid growth regulation, we have investigated the presence of IGF-1, as detected by means of radioimmuno assay and of immunocytochemistry, in thyrocytes from normal thyroid and from multinodular goiter. Our study revealed that IGF-1 is detectable in thyroid cells from multinodular goiter and, to a lesser extent, from normal thyroid. Both techniques used in this study demonstrated that thyrocytes are the site of accumulation of IGF-1 and that stromal cells contain lower amounts of this growth factor. The findings of the present study seem to suggest that thyrocytes could produce IGF-1 in vivo. This feature gives further support to the hypothesis that IGF-1 may regulate thyroid growth and therefore it might be involved in the pathogenesis of multinodular goiter.

Autocrine growth factors produced in the thyroid

This catalogue of autocrine growth factors is limited to proteins--metabolites of iodine and prostaglandins are omitted and they are undoubtedly of autocrine importance in the thyroid, as elsewhere. However, this summary of polypeptide growth factors secreted by the thyroid illustrates the potential cells have to condition their environment to modify their responses to external stimuli. This enables cells in different tissues to respond to agonists in different ways. The effects of TSH on IGF, IGFBP and IGF receptor production and the effects of IGFBPs on IGF action are good examples of this amplified response. Many pieces of the jigsaw, however, remain to be found and put in place before a clear picture of the regulation and roles of these factors can be made.

Basic fibroblast growth factor (basic FGF) in isolated ovine thyroid follicles: thyrotropin stimulation and effects of basic FGF on DNA synthesis, iodine uptake and organification, and the release of insulin-like growth factors (IGFs) and IGF-binding proteins

We examined the effects of thyroid-stimulating hormone (TSH) on basic fibroblast growth factor (basic FGF) expression in isolated ovine thyroid follicles in vitro, and the effects of exogenous basic FGF on thyroid growth and function, to elucidate the significance of increased basic FGF expression during TSH-induced rat thyroid hyperplasia in vivo. Primary cultures of ovine thyroid follicles were maintained in serum-free Ham's modified F-12M medium containing transferrin, somatostatin, and glycyl-histidyl-lysine (designated 3H) with or without basic FGF alone, or in combination with TSH (100 microU/mL) and cortisol (10 nM). Following 48 h incubation, cells were harvested and total RNA prepared for the detection of basic FGF mRNA using Northern blot analysis and ribonuclease protection assay. Basic FGF in the cytoplasm and extracellular matrix fractions was quantified by radioimmunoassay. Basic FGF mRNA transcripts of 3.7, 3.0, and 2.2 kb, respectively, were found in thyroid follicles cultured in 3H medium, and the abundance of each increased between 2- and 3-fold following incubation with 10-50 microU/mL TSH, although higher concentrations of TSH were less effective. Similar results were seen using a more sensitive ribonuclease protection assay. Cells cultured in control, 3H medium contained 2.4 +/- 0.5 fmol immunoreactive basic FGF/micrograms cell DNA within the cytoplasm and 21.1 +/- 1.5 fmol/micrograms DNA within the extracellular matrix (mean +/- SD, n = 6). A significant increase (p < 0.05) in basic FGF content was seen in both cell compartments following incubation with 50 or 100 microU/mL TSH, while 250 microU/mL was less effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered expression of insulin-like growth factor-I (IGF-I) and IGF binding proteins during rat thyroid hyperplasia and involution

We have investigated changes in the synthesis and localization of insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBPs) in thyroid tissues during the induction of goitre in iodine-deficient rats, and during the subsequent involution of the gland following goitrogen withdrawal. Goitre was induced in adult rats by acute (1 or 2 weeks) or chronic (4 or 10 weeks) administration of methimazole together with a low iodine diet. After twelve weeks the goitrogenic stimuli were removed and thyroids examined 4 weeks later. Circulating T4 levels became undetectable within two weeks of goitrogen administration while thyroid weight had increased five-fold. The thyroids continued to increase in size up to 10 weeks, but at a slower growth rate. IGF-I mRNA, detected by ribonuclease protection assay, was present in the control rat thyroid and increased in abundance after both 1 and 2 weeks of goitrogen administration. Levels of IGF-I mRNA showed a relative decline with prolonged goitrogen administration, and following thyroid involution the hybridization signal was similar to that seen in control glands. Northern blot hybridization showed that IGFBP-2, -3 and -5 mRNAs were all present in growth-quiescent, control thyroids and those encoding IGFBP-2 and -3 were elevated in the goitrous glands and remained so as long as goitrogen was administered, thereafter declining during thyroid involution. IGF-I and IGFBP-2 and -3 mRNAs and synthesized peptides, detected by in situ hybridization and immunohistochemistry respectively, were found to co-localize predominantly in follicular epithelial cells. IGFBP-5 mRNA abundance was unaltered during goitre formation, but was increased in the involuting thyroid. Both IGFBP-5 mRNA and peptide were localized to the parafollicular cells (C-cells) which were increased in number during involution. The results suggest that an increased expression of IGF-1 may contribute to early goitre formation, but that a relative increase in the abundance of IGFBP-2 and -3 may limit IGF availability at later times, and facilitate a slowing of thyroid growth rate. The discrete expression of IGFBP-5 by C-cells suggests that it could contribute indirectly to goitre formation or involution by acting in a paracrine fashion.

Molecular basis for the autoreactivity against thyroid stimulating hormone receptor

The present report identifies an important immunogenic region of the TSH receptor and determinants on the TSH receptor for the two types of autoantibodies seen in hyperthyroid Graves' disease and hypothyroid idiopathic myxedema, TSAbs and TSBAbs, respectively. The immunogenic domain with no important functional determinants, is contained within residues 303-382 and involves residues 352-366 in particular. There are determinants flanking the immunogenic domain on the C-terminal portion of the receptor which are the TSBAb and high affinity TSH binding sites: residues 295-306, 387-395, and tyrosine 385. Determinants on the N-terminal portion of the external domain, centered on residues 38-45, are TSAb interactions linked to low affinity TSH binding important for signal generation: threonine 40 and residues 30-33, 34-37, 42-45, 52-56, and 58-61. These determinants are conserved in human and rat receptors, are not present in gonadotropin receptors, and are each related to separate actions of TSH: binding vs. signal generation. They can, therefore, account for organ specific autoimmunity and the different disease expression effected by TSBAbs vs TSAbs, i.e. hypo- vs. hyperthyroidism, respectively. It is proposed that, in the thyroid, hormonal (TSH, insulin, hydrocortisone, IGF-I) suppression of class I genes might be one means of preserving self-tolerance in the face of the hormone action to increase the expression of tissue specific genes such as thyroglobulin and thyroid peroxidase. Inappropriately high class I expression in the thyroid, i.e. if induced by interferon, viruses, or some as yet unknown agent, would contribute to the generation of autoimmune disease. Thus, it would result in increased antigen presentation to the immune system, particularly those autoantigens increased by TSH and its cAMP signal such as thyroglobulin or thyroid peroxidase, or whose turnover is increased by TSH and its cAMP signal, such as the TSH receptor. In the case of the latter, peptide 352-366, known to be near a protease sensitive site on the receptor [41,49], would now act as a potent self-antigen and induce the formation of receptor autoantibodies. It is further proposed that methimazole and high doses of iodide are therapeutically effective agents in thyroid autoimmune disease because they, in part, decrease MHC class I gene expression. Speculation is presented which suggests that elimination of negative regulation of MHC class I and the TSH receptor is an important factor in the development of autoimmune thyroid disease.(ABSTRACT TRUNCATED AT 400 WORDS)