Nongenomic actions of thyroid hormone

Thyroid hormone analogues: Promising therapeutic avenues to improve the neurodevelopmental outcomes of intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a pregnancy complication impairing fetal growth and development. The compromised development is often attributed to disruptions of oxygen and nutrient supply from the placenta, resulting in a number of unfavourable physiological outcomes with impaired brain and organ growth. IUGR is associated with compromised development of both grey and white matter, predisposing the infant to adverse neurodevelopmental outcomes, including long-lasting cognitive and motor difficulties. Cerebral thyroid hormone (TH) signalling, which plays a crucial role in regulating white and grey matter development, is dysregulated in IUGR, potentially contributing to the neurodevelopmental delays associated with this condition. Notably, one of the major TH transporters, monocarboxylate transporter-8 (MCT8), is deficient in the fetal IUGR brain. Currently, no effective treatment to prevent or reverse IUGR exists. Management strategies involve close antenatal monitoring, management of maternal risk factors if present and early delivery if IUGR is found to be severe or worsening in utero. The overall goal is to determine the most appropriate time for delivery, balancing the risks of preterm birth with further fetal compromise due to IUGR. Drug candidates have shown either adverse effects or little to no benefits in this vulnerable population, urging further preclinical and clinical investigation to establish effective therapies. In this review, we discuss the major neuropathology of IUGR driven by uteroplacental insufficiency and the concomitant long-term neurobehavioural impairments in individuals born IUGR. Importantly, we review the existing clinical and preclinical literature on cerebral TH signalling deficits, particularly the impaired expression of MCT8 and their correlation with IUGR. Lastly, we discuss the current evidence on MCT8-independent TH analogues which mimic the brain actions of THs by being metabolised in a similar manner as promising, albeit underappreciated approaches to promote grey and white matter development and improve the neurobehavioural outcomes following IUGR.

The role of hormones in sepsis: an integrated overview with a focus on mitochondrial and immune cell dysfunction

Sepsis is a dysregulated host response to infection that results in life-threatening organ dysfunction. Virtually every body system can be affected by this syndrome to greater or lesser extents. Gene transcription and downstream pathways are either up- or downregulated, albeit with considerable fluctuation over the course of the patient's illness. This multi-system complexity contributes to a pathophysiology that remains to be fully elucidated. Consequentially, little progress has been made to date in developing new outcome-improving therapeutics. Endocrine alterations are well characterised in sepsis with variations in circulating blood levels and/or receptor resistance. However, little attention has been paid to an integrated view of how these hormonal changes impact upon the development of organ dysfunction and recovery. Here, we present a narrative review describing the impact of the altered endocrine system on mitochondrial dysfunction and immune suppression, two interlinked and key aspects of sepsis pathophysiology.

Comparative Analysis of Transcriptome Profiles Reveals Distinct and Organ-Dependent Genomic and Nongenomic Actions of Thyroid Hormone in Xenopus tropicalis Tadpoles

Background: Thyroid hormone (triiodothyronine [T3]) is essential for development and organ metabolism in all vertebrates. T3 has both genomic and nongenomic effects on target cells. While much has been learnt on its genomic effects via T3 receptors (TRs) in vertebrate development, mostly through TR-knockout and TR-knockin studies, little is known about the effects of T3 on gene expression in animals in the absence of TR. We have been studying Xenopus metamorphosis as a model for mammalian postembryonic development, a period around birth when plasma T3 level peaks and many organs/tissues mature into their adult forms. We have recently generated TR double knockout (TRDKO) Xenopus tropicalis animals. This offers an opportunity to compare the effects of T3 on global gene expression in tadpole tissues in the presence or absence of TR. Methods: We analyzed the effects of T3 on gene expression in tadpole tail and intestine by using RNA-seq analysis on wild-type and TRDKO tadpoles with or without T3 treatment. Results: We observed that removing TRs reduced the number of genes regulated by T3 in both organs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that T3 affected distinct biological processes and pathways in wild-type and TRDKO tadpoles. Many GO terms and KEGG pathways that were enriched among genes regulated in wild-type tissues are likely involved in mediating the effects of T3 on metamorphosis, for example, those related to development, stem cells, apoptosis, and cell cycle/cell proliferation. However, such GO terms and pathways were not enriched among T3-regulated genes in TRDKO tadpoles. Instead, in TRDKO tadpoles, GO terms and pathways related to "metabolism" and "immune response" were highly enriched among T3-regulated genes. We further observed strong divergence in the TR-independent nongenomic effects of T3 in the intestine and tail. Conclusions: Our data suggest that T3 has distinct and organ-dependent effects on gene expression in developing tadpoles. The TR-mediated effects are consistent with the metamorphic changes, in agreement with the fact that TR is necessary and sufficient to mediate the effects of T3 on metamorphosis. T3 appears to have a major effect on metabolism and immune response via TR-independent nongenomic processes.

Essential and subtype-dependent function of thyroid hormone receptors during Xenopus metamorphosis

Thyroid hormone (T3) plays critical roles in organ metabolism and development in vertebrates. Anuran metamorphosis is perhaps the most dramatic and best studied developmental process controlled by T3. Many changes in different organs/tissues during anuran metamorphosis resemble the maturation/remodeling of the corresponding organs/tissues during mammalian postembryonic development. The plasma T3 level peaks during both anuran metamorphosis and mammalian postembryonic development. T3 exerts its developmental function through transcriptional regulation via T3 receptors (TRs). Studies on the metamorphosis of two highly related anurans, pseudo-tetraploid Xenopus laevis and diploid Xenopus tropicalis, have led to a dual function model for TRs during development. This has been supported by strong molecular and genetic evidence. Here we review some of the evidence with a focus on more recent gene knockout studies in Xenopus tropicalis. These studies have not only supported the model but also revealed novel and TR subtype-specific roles during Xenopus development, particularly a critical role of TRα in controlling developmental timing and rate.

Thyroid and Corticosteroid Signaling in Amphibian Metamorphosis

In multicellular organisms, development is based in part on the integration of communication systems. Two neuroendocrine axes, the hypothalamic–pituitary–thyroid and the hypothalamic–pituitary–adrenal/interrenal axes, are central players in orchestrating body morphogenesis. In all vertebrates, the hypothalamic–pituitary–thyroid axis controls thyroid hormone production and release, whereas the hypothalamic–pituitary–adrenal/interrenal axis regulates the production and release of corticosteroids. One of the most salient effects of thyroid hormones and corticosteroids in post-embryonic developmental processes is their critical role in metamorphosis in anuran amphibians. Metamorphosis involves modifications to the morphological and biochemical characteristics of all larval tissues to enable the transition from one life stage to the next life stage that coincides with an ecological niche switch. This transition in amphibians is an example of a widespread phenomenon among vertebrates, where thyroid hormones and corticosteroids coordinate a post-embryonic developmental transition. The review addresses the functions and interactions of thyroid hormone and corticosteroid signaling in amphibian development (metamorphosis) as well as the developmental roles of these two pathways in vertebrate evolution.

Thyroid hormone regulates abrupt skin morphogenesis during zebrafish postembryonic development

Thyroid hormone is a key regulator of post-embryonic vertebrate development. Skin is a biomedically important thyroid hormone target organ, but the cellular and molecular mechanisms underlying skin pathologies associated with thyroid dysfunction remain obscure. The transparent skin of zebrafish is an accessible model system for studying vertebrate skin development. During post-embryonic development of the zebrafish, scales emerge in the skin from a hexagonally patterned array of dermal papillae, like other vertebrate skin appendages such as feathers and hair follicles. We show here that thyroid hormone regulates the rate of post-embryonic dermal development through interaction with nuclear hormone receptors. This couples skin development with body growth to generate a well ordered array of correctly proportioned scales. This work extends our knowledge of thyroid hormone actions on skin by providing in-vivo evidence that thyroid hormone regulates multiple aspects of dermal development.

Mechanism of PKM2 affecting cancer immunity and metabolism in Tumor Microenvironment

PKM2 is the enzyme that regulates the final rate-limiting step of glycolysis. PKM2 expression can reinforce the utilization of oxygen and synthesis of growth substances in cancer cells by enhancing OXPHOS and the Warburg effect. In cancer immunity, PKM2 can modulate the expression of PD-L1 in M2 macrophage and decrease the amount and activity of CD8+ T cells. This affects cancer cell killing and immune escape sequentially. How PKM2 regulates PD-L1 expression through immunometabolism is summarized. PKM2 builds a bridge between energy metabolism and cancer immunity. The activator and inhibitor of PKM2 both promote the anti-cancer immune response and inhibit cancer growth and metastasis by regulating the metabolism of cancer cells and immune cells in the tumor microenvironment through HIF-1α/PKM2 pathway. This review focuses on the precise role of PKM2 modulating immunometabolism, providing valuable suggestions for further study in this field.

Life Without Thyroid Hormone Receptor

Thyroid hormone (T3) is critical not only for organ function and metabolism in the adult but also for animal development. This is particularly true during the neonatal period when T3 levels are high in mammals. Many processes during this postembryonic developmental period resemble those during amphibian metamorphosis. Anuran metamorphosis is perhaps the most dramatic developmental process controlled by T3 and affects essentially all organs/tissues, often in an organ autonomous manner. This offers a unique opportunity to study how T3 regulates vertebrate development. Earlier transgenic studies in the pseudo-tetraploid anuran Xenopus laevis revealed that T3 receptors (TRs) are necessary and sufficient for mediating the effects of T3 during metamorphosis. Recent gene knockout studies with gene-editing technologies in the highly related diploid anuran Xenopus tropicalis showed, surprisingly, that TRs are not required for most metamorphic transformations, although tadpoles lacking TRs are stalled at the climax of metamorphosis and eventually die. Analyses of the changes in different organs suggest that removal of TRs enables premature development of many adult tissues, likely due to de-repression of T3-inducible genes, while preventing the degeneration of tadpole-specific tissues, which is possibly responsible for the eventual lethality. Comparison with findings in TR knockout mice suggests both conservation and divergence in TR functions, with the latter likely due to the greatly reduced need, if any, to remove embryo/prenatal-specific tissues during mammalian postembryonic development.

Role of thyroid hormones in normal and abnormal central nervous system myelination in humans and rodents

Thyroid hormones (THs) are instrumental in promoting the molecular mechanisms which underlie the complex nature of neural development and function within the central nervous system (CNS) in vertebrates. The key neurodevelopmental process of myelination is conserved between humans and rodents, of which both experience peak fetal TH concentrations concomitant with onset of myelination. The importance of supplying adequate levels of THs to the myelin producing cells, the oligodendrocytes, for promoting their maturation is crucial for proper neural function. In this review we examine the key TH distributor and transport proteins, including transthyretin (TTR) and monocarboxylate transporter 8 (MCT8), essential for supporting proper oligodendrocyte and myelin health; and discuss disorders with impaired TH signalling in relation to abnormal CNS myelination in humans and rodents. Furthermore, we explore the importance of using novel TH analogues in the treatment of myelination disorders associated with abnormal TH signalling.

The development of adult intestinal stem cells: Insights from studies on thyroid hormone-dependent anuran metamorphosis

Vertebrates organ development often takes place in two phases: initial formation and subsequent maturation into the adult form. This is exemplified by the intestine. In mouse, the intestine at birth has villus, where most differentiated epithelial cells are located, but lacks any crypts, where adult intestinal stem cells reside. The crypt is formed during the first 3 weeks after birth when plasma thyroid hormone (T3) levels are high. Similarly, in anurans, the intestine undergoes drastic remodeling into the adult form during metamorphosis in a process completely dependent on T3. Studies on Xenopus metamorphosis have revealed important clues on the formation of the adult intestine during metamorphosis. Here we will review our current understanding on how T3 induces the degeneration of larval epithelium and de novo formation of adult intestinal stem cells. We will also discuss the mechanistic conservations in intestinal development between anurans and mammals.

Iodine Deficiency Increases Fat Contribution to Energy Expenditure in Male Mice

More than a billion people worldwide are at risk of iodine deficiency (ID), with well-known consequences for development of the central nervous system. Furthermore, ID has also been associated with dyslipidemia and obesity in humans. To further understand the metabolic consequences of ID, here we kept 8-week-old C57/Bl6 mice at thermoneutrality (~28°C) while feeding them on a low iodine diet (LID). When compared with mice kept on control diet (LID + 0.71 μg/g iodine), the LID mice exhibited marked reduction in T4 and elevated plasma TSH, without changes in plasma T3 levels. LID mice grew normally, and had normal oxygen consumption, ambulatory activity, and heart expression of T3-responsive gene, confirming systemic euthyroidism. However, LID mice exhibited ~5% lower respiratory quotient (RQ), which reflected a ~2.3-fold higher contribution of fat to energy expenditure. LID mice also presented increased circulating levels of nonesterified fatty acids, ~60% smaller fat depots, and increased hepatic glycogen content, all indicative of accelerated lipolysis. LID mice responded much less to forced mobilization of energy substrates (50% food restriction for 3 days or starvation during 36 hours) because of limited size of the adipose depots. A 4-day treatment with T4 restored plasma T4 and TSH levels in LID mice and normalized RQ. We conclude that ID accelerates lipolysis and fatty acid oxidation, without affecting systemic thyroid hormone signaling. It is conceivable that the elevated plasma TSH levels trigger these changes by directly activating lipolysis in the adipose tissues.

The Role of Thyroid Diseases and their Medications in Cardiovascular Disorders: A Review of the Literature

The association between thyroid disease and cardiovascular manifestations is significant and undeniable. Previous studies have explained several aspects of the effects of thyroid hormone on the heart and cardiovascular system. Accordingly, both hyper and hypothyroidism can cause important alterations in cardiac rhythm, output and contractility as well as vascular resistance and blood pressure. Since treating the thyroid abnormality, especially in its initial stages, could lead to a significant improvement in most of its resultant cardiovascular disturbances, early suspicion and recognition of thyroid dysfunction, is necessary in patients with cardiovascular manifestations. In this in-depth review, we discuss the physiological roles as well as the effects of abnormal levels of thyroid hormones on the cardiovascular system. We also review the effects of the medications used for the treatment of hyper and hypothyroidism on cardiac function. In the end, we discuss the association between thyroid function and amiodarone, an effective and frequently-used antiarrhythmic drug, because of its well-known effects on the thyroid.

PKM2, function and expression and regulation

Pyruvate kinase (PK), as one of the key enzymes for glycolysis, can encode four different subtypes from two groups of genes, although the M2 subtype PKM2 is expressed mainly during embryonic development in normal humans, and is closely related to tissue repair and regeneration, with the deepening of research, the role of PKM2 in tumor tissue has received increasing attention. PKM2 can be aggregated into tetrameric and dimeric forms, PKM2 in the dimer state can enter the nuclear to regulate gene expression, the transformation between them can play an important role in tumor cell energy supply, epithelial-mesenchymal transition (EMT), invasion and metastasis and cell proliferation. We will use the switching effect of PKM2 in glucose metabolism as the entry point to expand and enrich the Warburg effect. In addition, PKM2 can also regulate each other with various proteins by phosphorylation, acetylation and other modifications, mediate the different intracellular localization of PKM2 and then exert specific biological functions. In this paper, we will illustrate each of these points.

Molecular functions and clinical impact of thyroid hormone-triggered autophagy in liver-related diseases

The liver is controlled by several metabolic hormones, including thyroid hormone, and characteristically displays high lysosomal activity as well as metabolic stress-triggered autophagy, which is stringently regulated by the levels of hormones and metabolites. Hepatic autophagy provides energy through catabolism of glucose, amino acids and free fatty acids for starved cells, facilitating the generation of new macromolecules and maintenance of the quantity and quality of cellular organelles, such as mitochondria. Dysregulation of autophagy and defective mitochondrial homeostasis contribute to hepatocyte injury and liver-related diseases, such as non-alcoholic fatty liver disease (NAFLD) and liver cancer.

Thyroid hormones (TH) mediate several critical physiological processes including organ development, cell differentiation, metabolism and cell growth and maintenance. Accumulating evidence has revealed dysregulation of cellular TH activity as the underlying cause of several liver-related diseases, including alcoholic or non-alcoholic fatty liver disease and liver cancer. Data from epidemiologic, animal and clinical studies collectively support preventive functions of THs in liver-related diseases, highlighting the therapeutic potential of TH analogs. Elucidation of the molecular mechanisms and downstream targets of TH should thus facilitate the development of therapeutic strategies for a number of major public health issues.

Here, we have reviewed recent studies focusing on the involvement of THs in hepatic homeostasis through induction of autophagy and their implications in liver-related diseases. Additionally, the potential underlying molecular pathways and therapeutic applications of THs in NAFLD and HCC are discussed.

Posttranscriptional actions of triiodothyronine on Tshb expression in TαT1 cells: New insights into molecular mechanisms of negative feedback

Rapid actions of triiodothyronine (T3) on thyrotropin (TSH) synthesis and secretion have been described in hypothyroid male rats. However, the molecular mechanisms remain unknown. TαT1 cells, a thyrotroph cell line, was used herein to characterize the possible non-genomic actions of T3 on the expression of alpha (Cga) and Tshb genes, and the posttranscriptional processing and translation of both transcripts. The involvement of αVβ3 integrin was also assessed. T3 quickly reduced Tshb mRNA content, poly(A) tail length and its association with ribosomes. The effect of T3 on Tshb gene expression was detected even in the presence of a transcription inhibitor. The decrease in Tshb mRNA content and polyadenylation depend on T3 interaction with αVβ3 integrin, while T3 reduced Cga mRNA content by transcriptional action. The translational rate of both transcripts was reduced by a mechanism, which does not depend on T3-αVβ3 integrin interaction. Results indicate that, in parallel with the inhibitory transcriptional action in Cga and Tshb gene expression, T3 rapidly triggers additional posttranscriptional mechanisms, reducing the TSH synthesis. These non-genomic actions partially depend on T3-αVβ3 integrin interaction at the plasma membrane of thyrotrophs and add new insights to the molecular mechanisms involved in T3 negative feedback loop.

Novel Transcriptional Mechanisms for Regulating Metabolism by Thyroid Hormone

The thyroid hormone plays a key role in energy and nutrient metabolisms in many tissues and regulates the transcription of key genes in metabolic pathways. It has long been believed that thyroid hormones (THs) exerted their effects primarily by binding to nuclear TH receptors (THRs) that are associated with conserved thyroid hormone response elements (TREs) located on the promoters of target genes. However, recent transcriptome and ChIP-Seq studies have challenged this conventional view as discordance was observed between TH-responsive genes and THR binding to DNA. While THR association with other transcription factors bound to DNA, TH activation of THRs to mediate effects that do not involve DNA-binding, or TH binding to proteins other than THRs have been invoked as potential mechanisms to explain this discrepancy, it appears that additional novel mechanisms may enable TH to regulate the mRNA expression. These include activation of transcription factors by SIRT1 via metabolic actions by TH, the post-translational modification of THR, the THR co-regulation of transcription with other nuclear receptors and transcription factors, and the microRNA (miR) control of RNA transcript expression to encode proteins involved in the cellular metabolism. Together, these novel mechanisms enlarge and diversify the panoply of metabolic genes that can be regulated by TH.

Role of Thyroid Hormone Receptor in Amphibian Development

The amphibian Xenopus laevis has long been used as a model for studying vertebrate cell and developmental biology largely due to the easiness to manipulate this system in vivo and in vitro. While most of the developmental studies have been on Xenopus embryogenesis, considerable efforts have been made to understand its metamorphosis, a process mimicking postembryonic development in mammals when many organs mature into their adult forms in the presence of high levels of thyroid hormone (T3). Amphibian metamorphosis is totally dependent on T3 and offers a number of advantages for experimental analyses compared to the late stage, uterus-enclosed mammalian embryos. Earlier studies on metamorphosis in Xenopus laevis have revealed dual functions of T3 receptors (TR) during premetamorphic development and metamorphosis as well as important roles of TR-interacting corepressors and coactivators during these two periods, respectively. The development of gene-editing technologies that functions in amphibians in recent years has made possible for the first time to study function of endogenous TRs, especially in the highly related diploid anuran species Xenopus tropicalis. Here, we first review the current mechanistic understanding of the regulation of metamorphosis by T3 and TR, and then describe a detailed method to use TALEN to knock out TRα for studying its role in gene regulation by T3 in vivo and Xenopus development.

Action of Thyroid Hormones, T3 and T2, on Hepatic Fatty Acids: Differences in Metabolic Effects and Molecular Mechanisms

The thyroid hormones (THs) 3,3′,5,5′-tetraiodo-l-thyronine (T4) and 3,5,3′-triiodo-l-thyronine (T3) influence many metabolic pathways. The major physiological function of THs is to sustain basal energy expenditure, by acting primarily on carbohydrate and lipid catabolism. Beyond the mobilization and degradation of lipids, at the hepatic level THs stimulate the de novo fatty acid synthesis (de novo lipogenesis, DNL), through both the modulation of gene expression and the rapid activation of cell signalling pathways. 3,5-Diiodo-l-thyronine (T2), previously considered only a T3 catabolite, has been shown to mimic some of T3 effects on lipid catabolism. However, T2 action is more rapid than that of T3, and seems to be independent of protein synthesis. An inhibitory effect on DNL has been documented for T2. Here, we give an overview of the mechanisms of THs action on liver fatty acid metabolism, focusing on the different effects exerted by T2 and T3 on the regulation of the DNL. The inhibitory action on DNL exerted by T2 makes this compound a potential and attractive drug for the treatment of some metabolic diseases and cancer.

Non-Neuronal Cells in the Hypothalamic Adaptation to Metabolic Signals

Although the brain is composed of numerous cell types, neurons have received the vast majority of attention in the attempt to understand how this organ functions. Neurons are indeed fundamental but, in order for them to function correctly, they rely on the surrounding "non-neuronal" cells. These different cell types, which include glia, epithelial cells, pericytes, and endothelia, supply essential substances to neurons, in addition to protecting them from dangerous substances and situations. Moreover, it is now clear that non-neuronal cells can also actively participate in determining neuronal signaling outcomes. Due to the increasing problem of obesity in industrialized countries, investigation of the central control of energy balance has greatly increased in attempts to identify new therapeutic targets. This has led to interesting advances in our understanding of how appetite and systemic metabolism are modulated by non-neuronal cells. For example, not only are nutrients and hormones transported into the brain by non-neuronal cells, but these cells can also metabolize these metabolic factors, thus modifying the signals reaching the neurons. The hypothalamus is the main integrating center of incoming metabolic and hormonal signals and interprets this information in order to control appetite and systemic metabolism. Hence, the factors transported and released from surrounding non-neuronal cells will undoubtedly influence metabolic homeostasis. This review focuses on what is known to date regarding the involvement of different cell types in the transport and metabolism of nutrients and hormones in the hypothalamus. The possible involvement of non-neuronal cells, in particular glial cells, in physiopathological outcomes of poor dietary habits and excess weight gain are also discussed.

Implication of thyroid hormone signaling in neural crest cells migration: Evidence from thyroid hormone receptor beta knockdown and NH3 antagonist studies

Thyroid hormones (TH) have been mainly associated with post-embryonic development and adult homeostasis but few studies report direct experimental evidence for TH function at very early phases of embryogenesis. We assessed the outcome of altered TH signaling on early embryogenesis using the amphibian Xenopus as a model system. Precocious exposure to the TH antagonist NH-3 or impaired thyroid receptor beta function led to severe malformations related to neurocristopathies. These include pathologies with a broad spectrum of organ dysplasias arising from defects in embryonic neural crest cell (NCC) development. We identified a specific temporal window of sensitivity that encompasses the emergence of NCCs. Although the initial steps in NCC ontogenesis appeared unaffected, their migration properties were severely compromised both in vivo and in vitro. Our data describe a role for TH signaling in NCCs migration ability and suggest severe consequences of altered TH signaling during early phases of embryonic development.

Pulmonary hypertension in thyroid diseases

The influence of thyroid hormones on cardiovascular system is well established. Thyroid diseases can effectively enhance the alteration on cardiovascular system by influencing chronotropic and inotropic actions of the heart; altering the strength and the speed of contraction, the speed of relaxation, the duration of the potential of action, and the duration of the refractory period and atrio-ventricular conduction time; modulating circulation and peripheral vascular beds. One of the more intriguing insights in the connection between thyroid diseases and cardiovascular alterations is related to the evaluation of the influence of thyroid hormones on pulmonary vascular beds. Literature reported several studies regarding the association between both hypothyroidism and hyperthyroidism and the occurrence of increased vascular pulmonary arterial pressure. Nevertheless, the pathogenetic mechanisms able to explain such relationship are not fully understood. Many doubts still persist in the comprehension of the mechanisms of pulmonary hypertension in thyroid diseases. The aim of this review was to provide possible explanation about the possible interaction between pulmonary vascular beds and thyroid function in order to evaluate the possibility of novel perspectives in the general management of patients suffering from thyroid and cardiovascular diseases.

Thyroid hormone regulation of adult intestinal stem cells: Implications on intestinal development and homeostasis

Organ-specific adult stem cells are essential for organ homeostasis, tissue repair and regeneration. The formation of such stem cells often takes place during postembryonic development, a period around birth in mammals when plasma thyroid hormone concentration is high. The life-long self-renewal of the intestinal epithelium has made mammalian intestine a valuable model to study the function and regulation and adult stem cells. On the other hand, much less is known about how the adult intestinal stem cells are formed during vertebrate development. Here, we will review some recent progresses on this subject, focusing mainly on the formation of the adult intestine during Xenopus metamorphosis. We will discuss the role of thyroid hormone signaling pathway in the process and potential molecular conservations between amphibians and mammals as well as the implications in organ homeostasis and human diseases.

Thyroxin Is Useful to Improve Sperm Motility

Background

The aim of this study was to evaluate the non-genomic action of thyroxin on sperm kinetic and its probable use to improve sperm recovery after applying an en- richment method like “swim-up” in comparison with the available one, pentoxifylline.

Materials and Methods

This is an experimental study. A total of 50 patients were re- cruited, followed by infertility consultation. Conventional sperm assays were performed according to World Health Organization criteria-2010 (WHO-2010). A Computer Aided Semen Analysis System was employed to assess kinetic parameters and concentrations. Number of the motile sperm recovered after preparation technique was calculated.

Results

Addition of T4 (0.002 µg/ml) to semen samples increased hypermotility at 20 minutes (control: 14.18 ± 5.1% vs. 17.66 ± 8.88%, P<0.03, data expressed as mean ± SD) and remained unchanged after 40 minutes. Significant differences were found in the motile sperm recovered after swim-up (control: 8.93×10⁶ ± 9.52× 06vs. 17.20×10⁶ ± 21.16×10⁶, P<0.03), achieving all of the tested samples a desirable threshold value for artificial insemination outcome, while adding pentoxifylline increased the number of recovered sperm after swim-up in 60% of the studied cases. No synergism between two treatments could be determined.

Conclusion

We propose a new physiological tool to artificially improve insemination. The discussion opens windows to investigate unknown pathways involved in sperm ca- pacitation and gives innovative arguments to better understand infertility mechanisms.

Regulation of growth rate and developmental timing by Xenopus thyroid hormone receptor α

Thyroid hormone (TH) is critical for vertebrate postembryonic development, a period around birth in mammals when plasma TH levels are high. Interestingly, TH receptors (TRs), especially TRα, are expressed prior to the synthesis and secretion of zygotic TH, suggesting the existence of unliganded TR during development. However, the role of unliganded TR during mammalian development has been difficult to study, in part due to the relatively weak phenotype of TR knockout mice. Amphibian metamorphosis resembles postembryonic development in mammals and is controlled by TH via TRs. Like in mammals, TRα gene is highly activated and is the major TR expressed prior to the synthesis of endogenous TH. By using TALEN (transcriptional activator like effector nucleases)-mediated gene editing approach, we and others have now shown that unliganded TRα has two independent functions during Xenopus premetamorphosis, i.e. inhibiting growth rate and slowing development. Furthermore, molecular and transgenic studies have shown that unliganded TRα accomplishes these via the recruitment of histone deacetylase (HDAC)-containing corepressor complexes to repress the expression of TH-inducible genes.

In vitro and in vivo activation of mitochondrial membrane permeability transition pore using triiodothyronine

Using a novel method for evaluating mitochondrial swelling (Drahota et al. 2012a) we studied the effect of calcium (Ca(2+)), phosphate (P(i)), and triiodothyronine (T(3)) on the opening of mitochondrial membrane permeability transition pore and how they interact in the activation of swelling process. We found that 0.1 mM P(i), 50 microM Ca(2+) and 25 microM T(3) when added separately increase the swelling rate to about 10 % of maximal values when all three factors are applied simultaneously. Our findings document that under experimental conditions in which Ca(2+) and P(i) are used as activating factors, the addition of T(3) doubled the rate of swelling. T(3) has also an activating effect on mitochondrial membrane potential. The T(3) activating effect was also found after in vivo application of T(3). Our data thus demonstrate that T(3) has an important role in opening the mitochondrial membrane permeability pore and activates the function of the two key physiological swelling inducers, calcium and phosphate ions.

Serum free thyroxine levels are positively associated with arterial stiffness in the SardiNIA study

OBJECTIVE

Thyroid dysfunction may accelerate atherosclerosis. Aortic pulse wave velocity (PWV) is an early index of arterial stiffness and an important risk factor for cardiovascular disease and might therefore be linked to changes in thyroid activity. We investigated the relationship between thyroid function and carotid-femoral PWV, as an index of arterial stiffness.

DESIGN

Cross-sectional cohort study.

PATIENTS

Participants from the SardiNIA study. Those being treated for thyroid diseases were excluded, yielding a sample of 5875 aged 14-102.

MEASUREMENTS

Clinical parameters, blood tests including serum TSH and serum FT4, and carotid-femoral PWV were measured.

RESULTS

After adjusting for confounders, a direct and linear association between FT4 and PWV was shown (multiple regression analysis). The model containing age, mean blood pressure, body mass index, heart rate, FT4, hypertension, diabetes and dyslipidaemia accounted for 55% of the variation in PWV.

CONCLUSIONS

Like several other known risk factors, serum FT4 levels are associated with carotid-femoral PWV, suggesting that high FT4 levels have a detrimental effect on aortic stiffness and may contribute to ageing process of the vascular system. This finding may help to understand the pathogenesis of cardiovascular disease and contribute to improve prevention therapy.

G protein-coupled receptors: extranuclear mediators for the non-genomic actions of steroids

Steroids hormones possess two distinct actions, a delayed genomic effect and a rapid non-genomic effect. Rapid steroid-triggered signaling is mediated by specific receptors localized most often to the plasma membrane. The nature of these receptors is of great interest and accumulated data suggest that G protein-coupled receptors (GPCRs) are appealing candidates. Increasing evidence regarding the interaction between steroids and specific membrane proteins, as well as the involvement of G protein and corresponding downstream signaling, have led to identification of physiologically relevant GPCRs as steroid extranuclear receptors. Examples include G protein-coupled receptor 30 (GPR30) for estrogen, membrane progestin receptor for progesterone, G protein-coupled receptor family C group 6 member A (GPRC6A) and zinc transporter member 9 (ZIP9) for androgen, and trace amine associated receptor 1 (TAAR1) for thyroid hormone. These receptor-mediated biological effects have been extended to reproductive development, cardiovascular function, neuroendocrinology and cancer pathophysiology. However, although great progress have been achieved, there are still important questions that need to be answered, including the identities of GPCRs responsible for the remaining steroids (e.g., glucocorticoid), the structural basis of steroids and GPCRs' interaction and the integration of extranuclear and nuclear signaling to the final physiological function. Here, we reviewed the several significant developments in this field and highlighted a hypothesis that attempts to explain the general interaction between steroids and GPCRs.

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

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 β-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 β-catenin knockout mice (KO). In fact, T3 induced β-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-3β, known to phosphorylate and eventually promote β-catenin degradation, or E-cadherin-β-catenin association. However, T3 treatment increased β-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-β-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 β-catenin activation. Thus, T3 may be of therapeutic relevance to stimulate β-catenin signaling to in turn induce regeneration in selected cases of hepatic insufficiency.

Thyroid hormone inhibition in L6 myoblasts of IGF-I-mediated glucose uptake and proliferation: new roles for integrin αvβ3

Thyroid hormones L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3) have been shown to initiate short- and long-term effects via a plasma membrane receptor site located on integrin αvβ3. Also insulin-like growth factor type I (IGF-I) activity is known to be subject to regulation by this integrin. To investigate the possible cross-talk between T4 and IGF-I in rat L6 myoblasts, we have examined integrin αvβ3-mediated modulatory actions of T4 on glucose uptake, measured through carrier-mediated 2-deoxy-[3H]-D-glucose uptake, and on cell proliferation stimulated by IGF-I, assessed by cell counting, [3H]-thymidine incorporation, and fluorescence-activated cell sorting analysis. IGF-I stimulated glucose transport and cell proliferation via the cell surface IGF-I receptor (IGFIR) and, downstream of the receptor, by the phosphatidylinositol 3-kinase signal transduction pathway. Addition of 0.1 nM free T4 caused little or no cell proliferation but prevented both glucose uptake and proliferative actions of IGF-I. These actions of T4 were mediated by an Arg-Gly-Asp (RGD)-sensitive pathway, suggesting the existence of crosstalk between IGFIR and the T4 receptor located near the RGD recognition site on the integrin. An RGD-sequence-containing integrin inhibitor, a monoclonal antibody to αvβ3, and the T4 metabolite tetraiodothyroacetic acid all blocked the inhibition by T4 of IGF-I-stimulated glucose uptake and cell proliferation. Western blotting confirmed roles for activated phosphatidylinositol 3-kinase and extracellular regulated kinase 1/2 (ERK1/2) in the effects of IGF-I and also showed a role for ERK1/2 in the actions of T4 that modified the effects of IGF-I. We conclude that thyroid hormone inhibits IGF-I-stimulated glucose uptake and cell proliferation in L6 myoblasts.

Hypothyroidism after a cancer diagnosis: etiology, diagnosis, complications, and management

Hypothyroidism is a common disease that is easily treated in the majority of cases, when readily diagnosed; however, presentation of an aggregate of its symptoms is often clinically overlooked or attributed to another disease and can potentially be lethal. Already prevalent in older women, its occurrence in younger patients is rising as a result of radiation therapy, radioactive iodine therapy, and newer antineoplastic agents used to manage various malignancies. The presence of nonspecific constitutional symptoms and neuropsychiatric complaints in cancer patients can be attributed to a myriad of other diagnoses and therapies. Thyroid dysfunction can be easily overlooked in cancer patients because of the complexity of cancer's clinical picture, particularly in the pediatric population. Underdiagnosis can have important consequences for the management of both hypothyroidism and the malignancy. At minimum, quality of life is adversely affected. Untreated hypothyroidism can lead to heart failure, psychosis, and coma and can reduce the effectiveness of potentially life-saving cancer therapies, whereas iatrogenic causes can provoke atrial fibrillation and osteoporosis. Consequently, the diagnosis and treatment of hypothyroidism in cancer patients are pertinent. We summarize the history, epidemiology, pathophysiology, clinical diagnosis, and management of hypothyroidism in cancer patients.

Triiodothyronine rapidly alters the TSH content and the secretory granules distribution in male rat thyrotrophs by a cytoskeleton rearrangement-independent mechanism

Rapid actions of T3 on TSH synthesis in posttranscriptional steps, such as polyadenylation and translation rate, have already been described. The focus of this paper was to characterize rapid actions of T3 on TSH secretion and the involvement of actin and microtubule cytoskeleton in this process. For that, sham-operated (SO) and thyroidectomized (Tx) rats were subjected to acute or chronic treatment with T3. We observed a disarrangement in microtubule and actin cytoskeletons and an increase in Tshb mRNA levels in Tx rats, whereas the total TSH protein content was reduced in the pituitary gland as a whole, but increased in the secretory granules close to the plasma membrane of thyrotrophs, as well as in the extracellular space. The acute T3 dose promoted a rapid increase and redistribution of TSH secretory granules throughout the cytoplasm, as well as a rearrangement in actin and microtubule cytoskeletons. The T3 chronic treatment outcome reinforces the acute effects observed and, additionally, evinces an increase in the α-tubulin content and a rearrangement in microtubule cytoskeleton. Thus, T3 is able to rapidly suppress TSH secretion and, in parallel, to promote a rearrangement in actin and microtubules assembly throughout the pituitary gland, effects that seem to be independent from each other.

Nrf2-regulated phase-II detoxification enzymes and phase-III transporters are induced by thyroid hormone in rat liver

Thyroid hormone (T₃)-induced calorigenesis triggers the hepatic production of reactive oxygen species (ROS) and redox-sensitive nuclear transcription factor erythroid 2-related factor 2 (Nrf2) activation. The aim of this study was to test the hypothesis that in vivo T₃ administration upregulates the expression of phase II and III detoxification proteins that is controlled by Nrf2. Male Sprague-Dawley rats were given a single intraperitoneal dose of 0.1 mg T₃/kg or T₃ vehicle (controls). After treatment, rectal temperature of the animals, liver Nrf2 DNA binding (EMSA), protein levels of epoxide hydrolase 1 (Eh1), NADPH-quinone oxidoreductase 1 (NQO1), glutathione-S-transferases Ya (GST Ya) and Yp (GST Yp), and multidrug resistance-associated proteins 2 (MRP-2) and 4 (MRP-4) (Western blot), and MRP-3 (RT-PCR) were determined at different times. T₃ significantly rose the rectal temperature of the animals in the time period studied, concomitantly with increases (P < 0.05) of liver Nrf2 DNA binding at 1 and 2 h after treatment, which was normalized at 4-12 h. Within 1-2 h after T₃ treatment, liver phase II enzymes Eh1, NQO1, GST Ya, and GST Yp were enhanced (P < 0.05) as did phase III transporters MRP-2 and MRP-3, whereas MRP-4 remained unchanged. In conclusion, enhancement of liver Nrf2 DNA binding elicited by in vivo T₃ administration is associated with upregulation of the expression of detoxification and drug transport proteins. These changes, in addition to antioxidant protein induction previously observed, may represent cytoprotective mechanisms underlying T₃ preconditioning against liver injury mediated by ROS and chemical toxicity.

New approaches to thyroid hormones and purinergic signaling

It is known that thyroid hormones influence a wide variety of events at the molecular, cellular, and functional levels. Thyroid hormones (TH) play pivotal roles in growth, cell proliferation, differentiation, apoptosis, development, and metabolic homeostasis via thyroid hormone receptors (TRs) by controlling the expression of TR target genes. Most of these effects result in pathological and physiological events and are already well described in the literature. Even so, many recent studies have been devoted to bringing new information on problems in controlling the synthesis and release of these hormones and to elucidating mechanisms of the action of these hormones unconventionally. The purinergic system was recently linked to thyroid diseases, including enzymes, receptors, and enzyme products related to neurotransmitter release, nociception, behavior, and other vascular systems. Thus, throughout this text we intend to relate the relationship between the TH in physiological and pathological situations with the purinergic signaling.

(Healthy) ageing: focus on iodothyronines

The activity of the thyroid gland diminishes during ageing, but a certain tissue reserve of T3 and its metabolites is maintained. This reserve is thought to play a regulatory role in energy homeostasis during ageing. This review critically assesses this notion. T3 was thought to act predominantly through pathways that require transcriptional regulation by thyroid hormone receptors (TRs). However, in recent years, it has emerged that T3 and its metabolites can also act through non-genomic mechanisms, including cytosolic signaling. Interestingly, differences may exist in the non-genomic pathways utilized by thyroid hormone metabolites and T3. For instance, one particular thyroid hormone metabolite, namely 3,5-diiodo-l-thyronine (T2), increases the activity of the redox-sensitive protein deacetylase SIRT1, which has been associated with improvements in healthy ageing, whereas evidence exists that T3 may have the opposite effect. Findings suggesting that T3, T2, and their signaling pathways, such as those involving SIRT1 and AMP-activated protein kinase (AMPK), are associated with improvements in diet-induced obesity and insulin resistance emphasize the potential importance of the thyroid during ageing and in ageing-associated metabolic diseases.

Exogenous T3 administration provides neuroprotection in a murine model of traumatic brain injury

Traumatic brain injury (TBI) induces primary and secondary damage in both the endothelium and the brain parenchyma. While neurons die quickly by necrosis, a vicious cycle of secondary injury in endothelial cells exacerbates the initial injury. Thyroid hormones are reported to be decreased in patients with brain injury. Controlled cortical impact injury (CCI) is a widely used, clinically relevant model of TBI. Here, using CCI in adult male mice, we set to determine whether 3,5,3'-triiodothyronine (T3) attenuates posttraumatic neurodegeneration and neuroinflammation in an experimental model of TBI. Treatment with T3 (1.2μg/100g body weight, i.p.) 1h after TBI resulted in a significant improvement in motor and cognitive recovery after CCI, as well as in marked reduction of lesion volumes. Mouse model for brain injury showed reactive astrocytes with increased glial fibrillary acidic protein, and formation of inducible nitric oxide synthase (iNOS). Western blot analysis revealed the ability of T3 to reduce brain trauma through modulation of cytoplasmic-nuclear shuttling of nuclear factor-κB (NF-κB). Twenty-four hours after brain trauma, T3-treated mice also showed significantly lower number of TUNEL(+) apoptotic neurons and curtailed induction of Bax, compared to vehicle control. In addition, T3 significantly enhanced the post-TBI expression of the neuroprotective neurotrophins (BDNF and GDNF) compared to vehicle. Our data provide an additional mechanism for the anti-inflammatory effects of thyroid hormone with critical implications in immunopathology at the cross-roads of the immune-endocrine circuits.

3,5-Diiodo-L-thyronine administration to hypothyroid rats rapidly enhances fatty acid oxidation rate and bioenergetic parameters in liver cells

Growing evidence shows that, among triiodothyronine derivatives, 3,5 diiodo-L-thyronine (T(2)) plays an important role in energy metabolism and fat storage. In the present study, short-term effects of T(2) administration to hypothyroid rats on fatty acid oxidation rate and bioenergetic parameters were investigated. Within 1 h following T(2) injection, state 3 and state 4 respiration rates, which were reduced in hypothyroid mitochondria, were noticeably increased particularly in succinate- with respect to glutamate/malate-energized mitochondria. Maximal respiratory activity, observed when glutamate/malate/succinate were simultaneously present in the respiratory medium, was significantly stimulated by T(2) treatment. A T(2)-induced increase in respiratory rates was also observed when palmitoyl-CoA or L-palmitoylcarnitine were used as substrates. No significant change in respiratory control index and ADP/O ratio was observed. The activities of the mitochondrial respiratory chain complexes, especially Complex II, were increased in T(2)-treated rats. In the latter, Complex V activities, assayed in both ATP synthesis and hydrolysis direction, were enhanced. The rate of fatty acid oxidation, followed by conversion of [(14)C]palmitate to CO(2) and ketone bodies, was higher in hepatocytes isolated from T(2)-treated rats. This increase occurs in parallel with the raise in the activity of carnitine palmitoyltransferase-I, the rate limiting enzyme of fatty acid β-oxidation, assayed in situ in digitonin-permeabilized hepatocytes. Overall, these results indicate that T(2) rapidly increases the ability of mitochondria to import and oxidize fatty acids. An emerging idea in the literature is the ability of T(2) to reduce adiposity and dyslipidemia and to prevent the development in liver steatosis. The results of the present study, showing a rapid T(2)-induced increase in the ability of mitochondria to import and oxidize fatty acids, may contribute to understand the biochemical mechanisms of T(2)-metabolic effects.

Unliganded thyroid hormone receptor regulates metamorphic timing via the recruitment of histone deacetylase complexes

Anuran metamorphosis involves a complex series of tissue transformations that change an aquatic tadpole to a terrestrial frog and resembles the postembryonic perinatal period in mammals. Thyroid hormone (TH) plays a causative role in amphibian metamorphosis and its effect is mediated by TH receptors (TRs). Molecular analyses during Xenopus development have shown that unliganded TR recruits histone deacetylase (HDAC)-containing N-CoR/SMRT complexes and causes histone deacetylation at target genes while liganded TR leads to increased histone acetylations and altered histone methylations at target genes. Transgenic studies involving mutant TR-cofactors have shown that corepressor recruitment by unliganded TR is required to ensure proper timing of the onset of metamorphosis while coactivator levels influence the rate of metamorphic progression. In addition, a number of factors that can influence cellular free TH levels appear to contribute the timing of metamorphic transformations of different organs by regulating the levels of unliganded vs. liganded TR in an organ-specific manner. Thus, the recruitment of HDAC-containing corepressor complexes by unliganded TR likely controls both the timing of the initiation of metamorphosis and the temporal regulation of organ-specific transformations. Similar mechanisms likely mediate TR function in mammals as the maturation of many organs during postembryonic development is dependent upon TH and resembles organ metamorphosis in amphibians.

TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis

This paper provides the reader with an overview of our current knowledge of hypothalamic-pituitary-thyroid feedback from a cybernetic standpoint. Over the past decades we have gained a plethora of information from biochemical, clinical, and epidemiological investigation, especially on the role of TSH and other thyrotropic agonists as critical components of this complex relationship. Integrating these data into a systems perspective delivers new insights into static and dynamic behaviour of thyroid homeostasis. Explicit usage of this information with mathematical methods promises to deliver a better understanding of thyrotropic feedback control and new options for personalised diagnosis of thyroid dysfunction and targeted therapy, also by permitting a new perspective on the conundrum of the TSH reference range.

Thyroid hormone receptor actions on transcription in amphibia: The roles of histone modification and chromatin disruption

Thyroid hormone (T3) plays diverse roles in adult organ function and during vertebrate development. The most important stage of mammalian development affected by T3 is the perinatal period when plasma T3 level peaks. Amphibian metamorphosis resembles this mammalian postembryonic period and is absolutely dependent on T3. The ability to easily manipulate this process makes it an ideal model to study the molecular mechanisms governing T3 action during vertebrate development. T3 functions mostly by regulating gene expression through T3 receptors (TRs). Studies in vitro, in cell cultures and reconstituted frog oocyte transcription system have revealed that TRs can both activate and repress gene transcription in a T3-dependent manner and involve chromatin disruption and histone modifications. These changes are accompanied by the recruitment of diverse cofactor complexes. More recently, genetic studies in mouse and frog have provided strong evidence for a role of cofactor complexes in T3 signaling in vivo. Molecular studies on amphibian metamorphosis have also revealed that developmental gene regulation by T3 involves histone modifications and the disruption of chromatin structure at the target genes as evidenced by the loss of core histones, arguing that chromatin remodeling is an important mechanism for gene activation by liganded TR during vertebrate development.

Thyroid hormone and the central control of homeostasis

It has long been known that thyroid hormone has profound direct effects on metabolism and cardiovascular function. More recently, it was shown that the hormone also modulates these systems by actions on the central autonomic control. Recent studies that either manipulated thyroid hormone signalling in anatomical areas of the brain or analysed seasonal models with an endogenous fluctuation in hypothalamic thyroid hormone levels revealed that the hormone controls energy turnover. However, most of these studies did not progress beyond the level of anatomical nuclei; thus, the neuronal substrates as well as the molecular mechanisms remain largely enigmatic. This review summarises the evidence for a role of thyroid hormone in the central autonomic control of peripheral homeostasis and advocates novel strategies to address thyroid hormone action in the brain on a cellular level.

An in vitro method to study the effects of thyroid hormone-disrupting chemicals on neuronal development

Thyroid hormones (THs) play critical roles for normal cerebellar development. It has been reported that several environmental chemicals may affect cerebellar development through TH system. One such example is the suppression of TH receptor (TR)-mediated transcription by polybrominated diphenyl ethers (PBDEs). To determine the effect of these chemicals on brain development, we established a primary culture system of rat cerebellar Purkinje cells. Using this system, as low as 10(-10)M TH induced Purkinje cell dendritic arborization and such effect was dose-dependent. We examined the effect of decabromodiphenyl ether (BDE209) using this system. Dendritic development of the Purkinje cells was suppressed by 10(-10)M BDE209, that was compatible to the result of the suppression of TR-mediated transcription by using reporter gene assay. These results suggest that TH plays a pivotal role in the development of the Purkinje cell dendrites. Together with in vitro assay system such as reporter gene assay and liquid chemiluminescent DNA-pull down assay, an in vitro protein-DNA binding assay, these assay systems provide us with precise information about environmental chemicals on brain development.

Oxidative stress and heart failure in altered thyroid States

Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism). The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.

Rapid steroid hormone actions initiated at the cell surface and the receptors that mediate them with an emphasis on recent progress in fish models

In addition to the classic genomic mechanism of steroid action mediated by activation of intracellular nuclear receptors, there is now extensive evidence that steroids also activate receptors on the cell surface to initiate rapid intracellular signaling and biological responses that are often nongenomic. Recent progress in our understanding of rapid, cell surface-initiated actions of estrogens, progestins, androgens and corticosteroids and the identities of the membrane receptors that act as their intermediaries is briefly reviewed with a special emphasis on studies in teleost fish. Two recently discovered novel proteins with seven-transmembrane domains, G protein-coupled receptor 30 (GPR30), and membrane progestin receptors (mPRs) have the ligand binding and signaling characteristics of estrogen and progestin membrane receptors, respectively, but their functional significance is disputed by some researchers. GPR30 is expressed on the cell surface of fish oocytes and mediates estrogen inhibition of oocyte maturation. mPRα is also expressed on the oocyte cell surface and is the intermediary in progestin induction of oocyte maturation in fish. Recent results suggest there is cross-talk between these two hormonal pathways and that there is reciprocal down-regulation of GPR30 and mPRα expression by estrogens and progestins at different phases of oocyte development to regulate the onset of oocyte maturation. There is also evidence in fish that mPRs are involved in progestin induction of sperm hypermotility and anti-apoptotic actions in ovarian follicle cells. Nonclassical androgen and corticosteroid actions have also been described in fish models but the membrane receptors mediating these actions have not been identified.

Free Triiodothyronine and Cholesterol Levels in Euthyroid Elderly T2DM Patients

Thyroid function regulates lipid metabolism. Despite the fact that T2DM is more prevalent in the elderly, often associates with thyroid dysfunction and increases cardiovascular risk both per se and via high TC and LDL-C levels, the association of the latter with FT(3) and FT(4) levels has not yet been fully investigated in T2DM. While trying to fill this gap in 296 elderly outpatients with T2DM, we found that TC and LDL-C correlated negatively with FT(4) and positively with FT(3). When divided according to treatment by oral hypoglycaemic agents (OHA) and insulin (IT), they reacted differently with respect to investigated associations: in the OHA's TC and LDL-C correlated negatively with FT(4) and showed no association with FT(3), whereas, in the IT's TC and LDL-C correlated positively with FT(3) and negatively with FT(4). When controlled for possible confounding factors, these associations did not change in the IT's but were missing in the OHA's. Recent literature reports upon complex hypothalamic and peripheral interactions between T2DM and thyroid, and suggests T(3) to enhance cholesterol synthesis and to have a role in insulin resistance states. Further investigations are needed to understand the intimate mechanisms of lipid metabolism in T2DM with respect to thyroid function.

3-Iodothyronamine metabolism and functional effects in FRTL5 thyroid cells

3-Iodothyronamine (T(1)AM), produced from thyroid hormones (TH) through decarboxylation and deiodination, is a potent agonist of trace amine-associated receptor 1 (TAAR1), a G protein-coupled receptor belonging to the family of TAARs. In vivo T(1)AM induces functional effects opposite to those produced on a longer time scale by TH and might represent a novel branch of TH signaling. In this study, we investigated the action of T(1)AM on thyroid and determined its uptake and catabolism using FRTL5 cells. The expression of TAAR1 was determined by PCR and western blot in FRTL5 cells, and cAMP, iodide uptake, and glucose uptake were measured after incubation with increasing concentrations of T(1)AM for different times. T(1)AM and its catabolites thyronamine (T(0)AM), 3-iodothyroacetic acid (TA(1)), and thyroacetic acid (TA(0)) were analyzed in FRTL5 cells by HPLC coupled to tandem mass spectrometry. The product of amplification of TAAR1 gene and TAAR1 protein was demonstrated in FRTL5 cells. No persistent and dose-dependent response to T(1)AM was observed after treatment with increasing doses of this substance for different times in terms of cAMP production and iodide uptake. A slight inhibition of glucose uptake was observed in the presence of 100 μM T(1)AM after 60 and 120 min (28 and 32% respectively), but the effect disappeared after 18 h. T(1)AM was taken up by FRTL5 cells and catabolized to T(0)AM, TA(1), and TA(0) confirming the presence of deiodinase and amine oxidase activity in thyroid. In conclusion, T(1)AM determined a slight inhibition of glucose uptake in FRTL5 cells, but it was taken up and catabolized by these cells.

Thyroid hormones as modulators of immune activities at the cellular level

BACKGROUND

Increasing evidence suggests that thyroid hormones, L-thyroxine (T(4)) and 3,3',5-triiodo-L-thyronine (T(3)), are modulators of the immune response. In monocytes, macrophages, leukocytes, natural killer cells, and lymphocytes, a wide range of immune functions such as chemotaxis, phagocytosis, generation of reactive oxygen species (ROS), and cytokine synthesis and release are altered under hypo- and hyperthyroid conditions.

SUMMARY

Hyperthyroidism decreases the proinflammatory activities of monocytes and macrophages, whereas enhancement of phagocytosis and increased levels of ROS may occur during hypothyroidism. The expression of proinflammatory molecules such as macrophage inflammatory protein-1α and interleukin-1β increases in hypothyroidism. However, in Kupffer cells, proinflammatory activities such as the respiratory burst, nitric oxide synthase activity, and tumor necrosis factor-α expression may result from increased T(3) levels. Thyroid hormones also affect natural killer cell activity and cell-mediated immune responses. Still, for many immune cells no clear correlation has been found so far between abnormally high or low T(3) or T(4) levels and the effects observed on the immune responses.

CONCLUSIONS

In this review we outline the contributions of thyroid hormones to different aspects of innate and adaptive immune responses. The relationship between thyroid hormones and immune cells is complex and T(3) and T(4) may modulate immune responses through both genomic and nongenomic mechanisms. Future studies of the molecular signaling mechanisms involved in this cross-talk between thyroid hormones and the immune system may support development of new strategies to improve clinical immune responses.