Thyroid hormone and thyroid hormone nuclear receptors: History and present state of art.

The present review traces the road leading to discovery of L-thyroxine, thyroid hormone (3,5,3´-triiodo-L-thyronine, T3) and its cognate nuclear receptors. Thyroid hormone is a pleio-tropic regulator of growth, differentiation, and tissue homeostasis in higher organisms. The major site of the thyroid hormone action is predominantly a cell nucleus. T3 specific binding sites in the cell nuclei have opened a new era in the field of the thyroid hormone receptors (TRs) discovery. T3 actions are mediated by high affinity nuclear TRs, TRalpha and TRbeta, which function as T3-activated transcription factors playing an essential role as transcription-modulating proteins affecting the transcriptional responses in target genes. Discovery and characterization of nuclear retinoid X receptors (RXRs), which form with TRs a heterodimer RXR/TR, positioned RXRs at the epicenter of molecular endocrinology. Transcriptional control via nuclear RXR/TR heterodimer represents a direct action of thyroid hormone. T3 plays a crucial role in the development of brain, it exerts significant effects on the cardiovascular system, skeletal muscle contractile function, bone development and growth, both female and male reproductive systems, and skin. It plays an important role in maintaining the hepatic, kidney and intestine homeostasis and in pancreas, it stimulates the beta-cell proliferation and survival. The TRs cross-talk with other signaling pathways intensifies the T3 action at cellular level. The role of thyroid hormone in human cancers, acting via its cognate nuclear receptors, has not been fully elucidated yet. This review is aimed to describe the history of T3 receptors, starting from discovery of T3 binding sites in the cell nuclei to revelation of T3 receptors as T3-inducible transcription factors in relation to T3 action at cellular level. It also focuses on milestones of investigation, comprising RXR/TR dimerization, cross-talk between T3 receptors, and other regulatory pathways within the cell and mainly on genomic action of T3. This review also focuses on novel directions of investigation on relationships between T3 receptors and cancer. Based on the update of available literature and the author's experimental experience, it is devoted to clinicians and medical students.

Effects of oral contraceptives on thyroid function and vice versa.

BACKGROUND: Thyroid gland dysfunction represents an epidemiologically relevant disease in the female gender, where treatment with oral contraceptives (OCs) is frequently prescribed. Although OCs are able to impact the thyroid gland function, scanty data have been released on this matter so far. AIM: The aim of this article was to review how hormonal OCs, including estrogen- or progesterone-only containing medications, interact with the hepatic production of thyroid-binding globulin (TBG) and, consequently, their effects on serum levels of thyroxine (T4) and triiodothyronine (T3). We also reviewed the effect of Levo-T4 (LT4) administration in women taking OCs and how they influence the thyroid function in both euthyroid women and in those receiving LT4. REVIEW: The estrogenic component of the pills is capable of increasing various liver proteins, such as TBG, sex hormone-binding protein (SHBG) and coagulation factors. On the other hand, the role of progestogens is to modulate estrogen-dependent effects mainly through their anti-androgenic action. In fact, a reduction in the effects of androgens is useful to keep the thromboembolic and cardiovascular risks low, whereas OCs increase it especially in women with subclinical hypothyroidism or in those treated with LT4. Accordingly, subclinical hypothyroidism is known to be associated with a higher mean platelet volume than normal and this increases cardiovascular risk due to platelet hyperactivity caused by incomplete thrombocytopoietic maturation.

How thyroid hormones and their inhibitors affect cartilage growth and shape in the frog Xenopus laevis.

Understanding how skeleton changes shape in ontogeny is fundamental to understanding how its shape diversifies in phylogeny. Amphibians pose a special case because their jaw and throat skeleton consists of cartilages that are dramatically reshaped midway through life to support new feeding and breathing styles. Although amphibian metamorphosis is commonly studied by immersing larvae in thyroid hormones (TH), how individual cartilages respond to TH is poorly understood. This study documents the effects of larval stage and TH type (T4 vs. T3), dose and deprivation on the size, shape and morphogenesis of the lower jaw and ceratohyal cartilages in the frog Xenopus laevis. It uses thyroid inhibitors to isolate the effects of each hormone at specific concentrations. It also deconstructs the TH responses into the effects on individual dimensions, and uses measures of percent change to eliminate the effects of body size and growth rate variation. As stage increases, T4 and T3 responses become increasingly similar to each other and to natural remodeling; the differences at low and intermediate stages result largely from abnormal responses to T3. Most notably, the beak-like lower jaw commonly observed at the lowest stage in other studies results largely from arrested growth of cartilage. TH responses are superimposed upon the growth typical for each stage so that cartilages can attain postmetamorphic shapes through dimensional changes that exceed those of natural metamorphosis. Using thyroid inhibitors alters the outcome of TH-induced remodeling, and T4 has almost the same capacity to induce metamorphic shape changes as T3. The results have implications for understanding how the starting shapes of larval elements affect morphogenesis, how chondrocytes behave to change cartilage shape, and how intracellular processing of TH might contribute to interspecific differences in shape change. Also, the data on animal mortality and which stages and doses most closely replicate natural remodeling have practical value for researchers who treat Xenopus tadpoles with TH.

Endocrinology and Pediatric Exercise Science-2016.

The Pediatric Exercise Science Year That Was section aims to highlight the most important (to the author's opinion) manuscripts that were published in 2016 in the field of endocrinology and pediatric exercise science. This year's selection includes studies showing that 1) Induction of T4 to T3 conversion by type 2 deiodinase following aerobic exercise in skeletal muscles was associated with concomitant increase in peroxisome proliferatoractivated receptor-γ coactivator-1α, and mitochondrial oxidative capacity and therefore plays an important mechanistic role in the muscle adaptation to exercise training. 2) Hypothyroidism in fetal and early postnatal life was associated with impaired spatial learning and memory and with reduced hippocampal brain-derived neurotrophic factor in male and female rat pups. Forced (treadmill) and voluntary (wheel) exercise alleviated all these biochemical and neuro-cognitive deficits. 3) The relationship between different exercise intensities and carbohydrate requirements to maintain euglycemia at basal insulin levels among adolescent and young adults with Type 1 diabetes are nonlinear but rather inverted- U with no exogenous glucose required to maintain stable glucose level at high-intensity exercise (80%). The implication of these studies to the pediatric population, their importance and the new research avenues that were opened by these studies is emphasized.

Thyroid hormone is required for pruning, functioning and long-term maintenance of afferent inner hair cell synapses.

Functional maturation of afferent synaptic connections to inner hair cells (IHCs) involves pruning of excess synapses formed during development, as well as the strengthening and survival of the retained synapses. These events take place during the thyroid hormone (TH)-critical period of cochlear development, which is in the perinatal period for mice and in the third trimester for humans. Here, we used the hypothyroid Snell dwarf mouse (Pit1(dw)) as a model to study the role of TH in afferent type I synaptic refinement and functional maturation. We observed defects in afferent synaptic pruning and delays in calcium channel clustering in the IHCs of Pit1(dw) mice. Nevertheless, calcium currents and capacitance reached near normal levels in Pit1(dw) IHCs by the age of onset of hearing, despite the excess number of retained synapses. We restored normal synaptic pruning in Pit1(dw) IHCs by supplementing with TH from postnatal day (P)3 to P8, establishing this window as being critical for TH action on this process. Afferent terminals of older Pit1(dw) IHCs showed evidence of excitotoxic damage accompanied by a concomitant reduction in the levels of the glial glutamate transporter, GLAST. Our results indicate that a lack of TH during a critical period of inner ear development causes defects in pruning and long-term homeostatic maintenance of afferent synapses.

L-thyroxine promotes a proliferative airway smooth muscle phenotype in the presence of TGF-ß1.

Hypothyroidism may reduce, whereas hyperthyroidism may aggravate, asthma symptoms. The mechanisms underlying this relationship are largely unknown. Since thyroid hormones have central roles in cell growth and differentiation, we hypothesized that airway remodeling, in particular increased airway smooth muscle (ASM) mass, may be involved. To address this hypothesis, we investigated the effects of triiodothyronine (T3) and l-thyroxine (T4) in the absence and presence of the profibrotic transforming growth factor (TGF)-ß1 on human ASM cell phenotype switching. T3 (1-100 nM) and T4 (1-100 nM) did not affect basal ASM proliferation. However, when combined with TGF-ß1 (2 ng/ml), T4 synergistically increased the proliferative response, whereas only a minor effect was observed for T3. In line with a switch from a contractile to a proliferative ASM phenotype, T4 reduced the TGF-ß1-induced contractile protein expression by ∼50%. Cotreatment with T3 reduced TGF-ß1-induced contractile protein expression by ∼25%. The synergistic increase in proliferation was almost fully inhibited by the integrin αvß3 antagonist tetrac (100 nM), whereas no significant effects of the thyroid receptor antagonist 1-850 (3 µM) were observed. Inhibition of MEK1/2, downstream of the integrin αvß3, also inhibited the T4- and TGF-ß1-induced proliferative responses. Collectively, the results indicate that T4, and to a lesser extent T3, promotes a proliferative ASM phenotype in the presence of TGF-ß1, which is predominantly mediated by the membrane-bound T4 receptor αvß3. These results indicate that thyroid hormones may enhance ASM remodeling in asthma, which could be of relevance for hyperthyroid patients with this disease.

Tri-iodothyronine induces hepatocyte proliferation by protein kinase A-dependent ß-catenin activation in rodents.

UNLABELLED: Thyroid hormone (T3), like many other ligands of the steroid/thyroid hormone nuclear receptor superfamily, is a strong inducer of liver cell proliferation in rats and mice. However, the molecular basis of its mitogenic activity, which is currently unknown, must be elucidated if its use in hepatic regenerative medicine is to be considered. F-344 rats or C57BL/6 mice were fed a diet containing T3 for 2-7 days. In rats, administration of T3 led to an increased cytoplasmic stabilization and nuclear translocation of ß-catenin in pericentral hepatocytes with a concomitant increase in cyclin-D1 expression. T3 administration to wild-type (WT) mice resulted in increased hepatocyte proliferation; however, no mitogenic response in hepatocytes to T3 was evident in the hepatocyte-specific ß-catenin knockout mice (KO). In fact, T3 induced ß-catenin-TCF4 reporter activity both in vitro and in vivo. Livers from T3-treated mice demonstrated no changes in Ctnnb1 expression, activity of glycogen synthase kinase-3ß, known to phosphorylate and eventually promote ß-catenin degradation, or E-cadherin-ß-catenin association. However, T3 treatment increased ß-catenin phosphorylation at Ser675, an event downstream of protein kinase A (PKA). Administration of PKA inhibitor during T3 treatment of mice and rats as well as in cell culture abrogated Ser675-ß-catenin and simultaneously decreased cyclin-D1 expression to block hepatocyte proliferation. CONCLUSION: We have identified T3-induced hepatocyte mitogenic response to be mediated by PKA-dependent ß-catenin activation. Thus, T3 may be of therapeutic relevance to stimulate ß-catenin signaling to in turn induce regeneration in selected cases of hepatic insufficiency.

Thyroid hormone deiodinases D1, D2, and D3 are expressed in human endothelial dermal microvascular line: effects of thyroid hormones.

Endothelial system acts as a large endocrine organ in the human body; however, little is still known about the regulative role of THs on endothelial cells. Aim of the present study was to investigate the expression of the TH deiodinases (D1, D2, and D3) and TH receptors (TRα1, TRα2, and TRß1) in an endothelial microvascular cultured cell model (HMEC-1), after stimulation with triiodothyronine (T3, 10-100 nM), thyroxine (T4, 10-100 nM), and reverse T3 (rT3, 1-10 nM). DIO1 was significantly inhibited by T4 at 10 and 100 nM (p < 0.001). rT3 significantly inhibited DIO1 at 1 nM concentration (p < 0.01) and stimulated DIO1 at 10 nM dosage (p < 0.001). T4 and rT3 significantly inhibited DIO2 at all concentrations. DIO3 was induced at 100 nM T3 (p < 0.05) and 100 nM rT3 (p < 0.01), and TRα1 and TRα2 mRNAs were significantly increased after 100 nM T3 treatment (p < 0.05) and decreased after 1 and 10 nM rT3 (p < 0.05). TRß1 was significantly increased by all THs at different concentrations: 10 nM T3 and 100 nM T3 (p < 0.05), 1 nM rT3 (p < 0.001), and 100 nM T4 (p < 0.01). D1 and D2 protein levels were evaluated, but no significant difference was observed for any hormonal treatment. For the first time, we found that the TH deiodinases and receptors are expressed in endothelial HMEC-1 cells. These findings might be of significant clinical relevance, given the important regulatory role of the endothelium as first barrier to the bloodstream.

Relationship between the thyroid axis and alcohol craving.

AIMS: A few studies have suggested a relationship between thyroid hormones and alcohol dependence (AD) such as a blunted increase of thyroid stimulating hormone (TSH) in response to thyrotropin-releasing hormone (TRH), lower levels of circulating free triiodothyronine (fT3) and free thyroxine (fT4) levels and down regulation of the TRH receptors. The current study aimed to explore the relationship between the hormones of the thyroid axis and alcohol-seeking behaviors in a sample of alcohol-dependent patients. METHODS: Forty-two treatment-seeking alcohol-dependent individuals enrolled in a 12-week treatment study were considered. The Timeline Follow Back (TLFB) was used to assess the number of drinks consumed during the 12-week period. Blood levels of thyroid hormones (TSH, fT3 and fT4) were measured prior to and at the end of treatment. Questionnaires were administered to evaluate craving for alcohol [Penn Alcohol Craving Scale (PACS) and the Obsessive Compulsive Drinking Scale (OCDS) and its two subscales ODS for obsessions and CDS for compulsions] as well as anxiety [State and Trait Inventory (STAI)], depression [the Zung Self-Rating Depression Scale (Zung)] and aggression [the Aggressive Questionnaire (AQ)]. RESULTS: At baseline, we found significant positive correlations between fT3 and OCDS (r = 0.358, P = 0.029) and CDS (r = 0.405, P = 0.013) and negative correlations between TSH levels and STAI (r = -0.342, P = 0.031), and AQ (r = -0.35, P = 0.027). At the end of the 12-week study period, abstinent patients had a greater change in TSH than those who relapsed (-0.4 vs. -0.25, F(1,24) = 5.4, P = 0.029). CONCLUSION: If confirmed in larger samples, these findings could suggest that the thyroid axis might represent a biomarker of alcohol craving and drinking.

The role of free triiodothyronine in pathogenesis of infertility in levothyroxine-treated women with thyroid autoimmunity - a preliminary observational study.

INTRODUCTION: The aim of this study was to analyze the possible role of free triiodothyronine (FT3) in infertility and in levothyroxine-treated (LT4) euthyroid women with Hashimoto thyroiditis (HT). METHODS: It is an observational retrospective case control study. Twenty one euthyroid women with HT on LT4 replacement therapy and a medical history of idiopathic infertility were included into the study. To achieve higher FT3 level, the dose of LT4 was increased in every patient. Fifteen fertile women with HT on LT4 replacement therapy served as a control group. RESULTS: At baseline in the study group mean thyroid stimulating hormone (TSH) level was 1.96 µU/ml ± 0.84 µU/ml and mean FT3 was 4.07 pmol/l ± 0.78 pmol/l. The mean TSH level after the increase of LT4 was 0.60 µU/ml ± 0.45 µU/ml (p < 0.0001), and the mean FT3 was 5.12 pmol/l ± 0.77 pmol/l (p = 0.0001). Baseline TSH in the study group was higher than in controls (p < 0.0001) and baseline FT3 in the study group was lower than in controls (p = 0.0003). CONCLUSIONS: Relatively low levels of FT3 in women with HT on LT4 replacement therapy may contribute to higher infertility rates.

Role of sirtuin 1 in the regulation of hepatic gene expression by thyroid hormone.

Sirtuin 1 (SIRT1) is a nuclear deacetylase that modulates lipid metabolism and enhances mitochondrial activity. SIRT1 targets multiple transcription factors and coactivators. Thyroid hormone (T(3)) stimulates the expression of hepatic genes involved in mitochondrial fatty acid oxidation and gluconeogenesis. We reported that T(3) induces genes for carnitine palmitoyltransferase (cpt1a), pyruvate dehydrogenase kinase 4 (pdk4), and phosphoenolpyruvate carboxykinase (pepck). SIRT1 increases the expression of these genes via the activation of several factors, including peroxisome proliferator-activated receptor α, estrogen-related receptor α, and peroxisome proliferator-activated receptor γ coactivator (PGC-1α). Previously, we reported that PGC-1α participates in the T(3) induction of cpt1a and pdk4 in the liver. Given the overlapping targets of T(3) and SIRT1, we investigated whether SIRT1 participated in the T(3) regulation of these genes. Resveratrol is a small phenolic compound whose actions include the activation of SIRT1. Addition of resveratrol increased the T(3) induction of the pdk4 and cpt1a genes in hepatocytes. Furthermore, expression of SIRT1 in hepatocytes mimicked resveratrol in the regulation of gene expression by T(3). The deacetylase activity of SIRT1 was required and PGC-1α was deacetylated following addition of T(3). We found that SIRT1 interacted directly with T(3) receptor (TRß). Knockdown of SIRT1 decreased the T(3) induction of cpt1a and pdk4 and reduced the T(3) inhibition of sterol response element binding protein (srebp-1c) both in isolated hepatocytes and in rat liver. Our results indicate that SIRT1 contributes to the T(3) regulation of hepatic genes.

Defending plasma T3 is a biological priority.

Triiodothyronine (T3), the active form of thyroid hormone is produced predominantly outside the thyroid parenchyma secondary to peripheral tissue deiodination of thyroxine (T4), with <20% being secreted directly from the thyroid. In healthy individuals, plasma T3 is regulated by the negative feedback loop of the hypothalamus-pituitary-thyroid axis and by homoeostatic changes in deiodinase expression. Therefore, with the exception of a minimal circadian rhythmicity, serum T3 levels are stable over long periods of time. Studies in rodents indicate that different levels of genetic disruption of the feedback mechanism and deiodinase system are met with increase in serum T4 and thyroid-stimulating hormone (TSH) levels, while serum T3 levels remain stable. These findings have focused attention on serum T3 levels in patients with thyroid disease, with important clinical implications affecting therapeutic goals and choice of therapy for patients with hypothyroidism. Although monotherapy with levothyroxine is the standard of care for hypothyroidism, not all patients normalize serum T3 levels with many advocating for combination therapy with levothyroxine and liothyronine. The latter could be relevant for a significant number of patients that remain symptomatic on monotherapy with levothyroxine, despite normalization of serum TSH levels.

Thyroid hormone actions in liver cancer.

The thyroid hormone 3,3',5-triiodo-L-thyronine (T3) mediates several physiological processes, including embryonic development, cellular differentiation, metabolism, and the regulation of cell proliferation. Thyroid hormone receptors (TRs) generally act as heterodimers with the retinoid X receptor (RXR) to regulate target genes. In addition to their developmental and metabolic functions, TRs have been shown to play a tumor suppressor role, suggesting that their aberrant expression can lead to tumor transformation. Conversely, recent reports have shown an association between overexpression of wild-type TRs and tumor metastasis. Signaling crosstalk between T3/TR and other pathways or specific TR coregulators appear to affect tumor development. Since TR actions are complex as well as cell context-, tissue- and time-specific, aberrant expression of the various TR isoforms has different effects during diverse tumorigenesis. Therefore, elucidation of the T3/TR signaling mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a summary of recent studies focusing on the role of TRs in hepatocellular carcinomas (HCCs).

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals.

Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.

Thyroid hormone drives fetal cardiomyocyte maturation.

Tri-iodo-l-thyronine (T(3)) suppresses the proliferation of near-term serum-stimulated fetal ovine cardiomyocytes in vitro. Thus, we hypothesized that T(3) is a major stimulant of cardiomyocyte maturation in vivo. We studied 3 groups of sheep fetuses on gestational days 125-130 (term ∼145 d): a T(3)-infusion group, to mimic fetal term levels (plasma T(3) levels increased from ∼0.1 to ∼1.0 ng/ml; t(1/2)∼24 h); a thyroidectomized group, to produce low thyroid hormone levels; and a vehicle-infusion group, to serve as intact controls. At 130 d of gestation, sections of left ventricular freewall were harvested, and the remaining myocardium was enzymatically dissociated. Proteins involved in cell cycle regulation (p21, cyclin D1), proliferation (ERK), and hypertrophy (mTOR) were measured in left ventricular tissue. Evidence that elevated T(3) augmented the maturation rate of cardiomyocytes included 14% increased width, 31% increase in binucleation, 39% reduction in proliferation, 150% reduction in cyclin D1 protein, and 500% increase in p21 protein. Increased expression of phospho-mTOR, ANP, and SERCA2a also suggests that T(3) promotes maturation and hypertrophy of fetal cardiomyocytes. Thyroidectomized fetuses had reduced cell cycle activity and binucleation. These findings support the hypothesis that T(3) is a prime driver of prenatal cardiomyocyte maturation.

AdipoR1 and AdipoR2 gene expression are regulated by thyroid hormones in adipose tissue.

The aim of this study was to examine whether the relative gene expression of AdipoR1 and AdipoR2 in rat adipose tissue is altered by thyroid hormones, and whether this might relate to their circulating thyroid hormones and adiponectin levels. Hyper- and hypothyroidism were induced by daily oral administration of levothyroxine and methimazole in rats, respectively, over a 42 days period. Real-time PCR analysis was performed to evaluate the changes in AdipoR1 and AdipoR2 mRNA levels in the adipose tissue on days 15, 28, 42, and also 2 weeks after the cessation of treatment. In response to treatment with methimazole, mRNA levels of AdipoR1 and AdipoR2 decreased in the white adipose tissue compared to the euthyroid rats (p < 0.05). This decline was reversible 2 weeks after treatment cessation. The mRNA levels of AdipoR1 and AdipoR2 were increased in the hyperthyroid group of animals compared to euthyroid control (p < 0.05), and its changes were reversible 2 weeks after treatment cessation (P < 0.05). Adiponectin receptors gene expression levels in the adipose tissue of treated animals have positive correlations with thyroid hormones concentrations. Our results suggest that AdipoR1 and AdipoR2 gene expression is regulated by thyroid hormones in hypo- and hyperthyroidism.

Partial sleep restriction modulates secretory activity of thyrotropic axis in healthy men.

Sleep and endocrine function are known to be closely related, but studies on the effect of moderate sleep loss on endocrine axes are still sparse. We examined the influence of partial sleep restriction for 2 days on the secretory activity of the thyrotropic axis. Fifteen healthy, normal-weight men were tested in a balanced, cross-over study. Serum concentrations of thyrotrophin (TSH), free triiodothyronine (fT3) and free thyroxine (fT4) were monitored at 1-h intervals during a 15-h daytime period (08:00-23:00 h) following two nights of restricted sleep (bedtime 02:45-07:00 h) and two nights of regular sleep (bedtime 22:45-07:00 h), respectively. Serum concentrations of fT3 (P < 0.026) and fT4 (P = 0.089) were higher after sleep restriction than regular sleep, with a subsequent blunting of TSH concentrations in the evening hours of the sleep restriction condition (P = 0.008). These results indicate profound alterations in the secretory activity of the thyrotropic axis after 2 days of sleep restriction to ~4 h, suggesting that acute partial sleep loss impacts endocrine homeostasis, with potential consequences for health and wellbeing.

Thyroid hormone exerts negative feedback on hypothalamic type 4 melanocortin receptor expression.

The type 4 melanocortin receptor MC4R, a key relay in leptin signaling, links central energy control to peripheral reserve status. MC4R activation in different brain areas reduces food intake and increases energy expenditure. Mice lacking Mc4r are obese. Mc4r is expressed by hypothalamic paraventricular Thyrotropin-releasing hormone (TRH) neurons and increases energy usage through activation of Trh and production of the thyroid hormone tri-iodothyronine (T(3)). These facts led us to test the hypothesis that energy homeostasis should require negative feedback by T(3) on Mc4r expression. Quantitative PCR and in situ hybridization showed hyperthyroidism reduces Mc4r mRNA levels in the paraventricular nucleus. Comparative in silico analysis of Mc4r regulatory regions revealed two evolutionarily conserved potential negative thyroid hormone-response elements (nTREs). In vivo ChIP assays on mouse hypothalamus demonstrated association of thyroid hormone receptors (TRs) with a region spanning one nTRE. Further, in vivo gene reporter assays revealed dose-dependent T(3) repression of transcription from the Mc4r promoter in mouse hypothalamus, in parallel with T(3)-dependent Trh repression. Mutagenesis of the nTREs in the Mc4r promoter demonstrated direct regulation by T(3), consolidating the ChIP results. In vivo shRNA knockdown, TR over-expression approaches and use of mutant mice lacking specific TRs showed that both TRalpha and TRbeta contribute to Mc4r regulation. T(3) repression of Mc4r transcription ensures that the energy-saving effects of T(3) feedback on Trh are not overridden by MC4R activation of Trh. Thus parallel repression by T(3) on hypothalamic Mc4r and Trh contributes to energy homeostasis.

Effects of 3, 5, 3'-triiodothyronine (t3) and follicle stimulating hormone on apoptosis and proliferation of rat ovarian granulosa cells.

Thyroid hormone (TH) is important for normal reproductive functions and dysregulation of TH support is associated with reproductive disorders. We have previously reported that 3,5,3'-triiodothyronine (T3) increases follicle stimulating hormone (FSH)-induced preantral follicle growth in vitro. Interaction of hormones with apoptosis and proliferation of granulosa cells is poorly understood. The present study investigated the role and the mechanism of T3 and/or FSH on granulosa cell apoptosis and proliferation. Granulosa cells harvested from DES-primed immature rats were exposed to T3 (1 nM) and/or FSH (100 ng/ml) for 24-48 h. We demonstrated by TUNEL assays that the hormones prevented cells from C8-ceramide-induced apoptosis. The Src/PI3K/Akt pathway was involved in the regulation of granulosa cell survival. While ineffective alone, T3 significantly enhanced the proliferating cell nuclear antigen (PCNA) content of FSH-induced granulosa cells, consistent with the cell number pattern after treatment. Moreover, the action of the hormones on cell proliferation was also shown to be mediated by the Src/PI3K/Akt pathway. Taken together, these results suggest that T3 potentiates the cell survival action of FSH through inhibiting cell apoptosis and promoting cell proliferation. Moreover, the protective and survival effects of hormones are mediated by the activation of Src/PI3K/Akt pathway.

[Endocrinological aspects of diabetes mellitus in the elderly].

Glucose-mediated energy production in central nervous system(CNS) reduces in the elderly. The reduction is also observed in young patients with diabetes mellitus(DM). Deviated endocrinological function is observed in both the elderly and young patients with DM. The deviation is characterized by mechanism of adaptation to the insufficient energy production in CNS. The decrease of glucose-mediated energy production is accelerated by decrease of the activity of growth hormone-insulin-like growth factor 1 axis and of conversion of thyroxine to triiodothyronine. These decreases are suitable for adaptation to the insufficient CNS activity induced by energy deficiency. Glucagon- and catecholamine-induced increases in plasma glucose level contribute to increase energy production. Parathyroid hormone action is activated in the elderly, which contributes to the inhibition of excess signal transduction in energy-deficient CNS. These deviations are considered as adaptations to the energy deficiency observed in aged patients with DM.