Genetic Background Strongly Influences the Impact of Carrying the Thr92Ala-DIO2 Polymorphism in the Male Mouse.

About half of the world population carries at least one allele of the Ala92-DIO2, which slows down the activity of the type 2 deiodinase (D2), the enzyme that activates T4 to T3. Carrying the Ala92-DIO2 allele has been associated with increased body mass index and insulin resistance, but this has not been reproduced in all populations. To test if the genetic background affects the impact of this polymorphism, here we studied the genetically distant C57Bl/6J (B6) and FVB/N (FVB) mice carrying the Ala92-Dio2 allele as compared to control mice carrying the Thr92-Dio2 allele. Whereas B6-Ala92-Dio2 and B6-Thr92-Dio2 mice-fed chow or high-fat diet-behaved metabolically similar in studies using indirect calorimetry, glucose- and insulin tolerance tests, and measuring white adipose tissue (WAT) weight and liver steatosis, major differences were observed between FVB-Ala92-Dio2 and FVB-Thr92-Dio2 mice: carrying the Ala92-Dio2 allele (on a chow diet) resulted in hypercholesterolemia, smaller WAT pads, hepatomegaly, steatosis, and transcriptome changes in the interscapular brown adipose tissue (iBAT) typical of ER stress and apoptosis. Acclimatization at thermoneutrality (30 °C) eliminated most of the metabolic phenotype, indicating that impaired adaptive (BAT) thermogenesis can be involved. In conclusion, the metabolic impact of carrying the Ala92-Dio2 allele depends greatly on the genetic background of the mouse, varying from no phenotype in B6 mice to a major phenotype in FVB mice. These results will help the planning of future clinical trials studying the Thr92Ala-DIO2 polymorphism and may explain why some clinical studies performed in different populations across the globe have obtained inconsistent results.

Factors and Mechanisms of Thyroid Hormone Activity in the Brain: Possible Role in Recovery and Protection.

Thyroid hormones (THs) are essential in normal brain development, and cognitive and emotional functions. THs act through a cascade of events including uptake by the target cells by specific cell membrane transporters, activation or inactivation by deiodinase enzymes, and interaction with nuclear thyroid hormone receptors. Several thyroid responsive genes have been described in the developing and in the adult brain and many studies have demonstrated a systemic or local reduction in TH availability in neurologic disease and after brain injury. In this review, the main factors and mechanisms associated with the THs in the normal and damaged brain will be evaluated in different regions and cellular contexts. Furthermore, the most common animal models used to study the role of THs in brain damage and cognitive impairment will be described and the use of THs as a potential recovery strategy from neuropathological conditions will be evaluated. Finally, particular attention will be given to the link observed between TH alterations and increased risk of Alzheimer's Disease (AD), the most prevalent neurodegenerative and dementing condition worldwide.

Deiodinase Type 3 Polymorphism (rs1190716) Affects Therapeutic Response to Levothyroxine.

Objectives: Levothyroxine (LT4) is a commonly used treatment for hypothyroidism. Deiodinase enzymes control the metabolism and homeostasis of thyroid hormones (THs). Deiodinase type 3 gene (DIO3) encodes deiodinase type 3 enzyme (D3), and the genetic polymorphisms of this gene could affect the levels of THs and the response to LT4 treatment. This study aimed to investigate the single-nucleotide polymorphism (SNP), rs1190716; C > T, of DIO3 as a candidate genetic variant that might affect the clinical response to LT4 treatment. Materials and Methods: Two hundred Iraqi hypothyroid female patients aged 40 years were enrolled in this cross-sectional study. All of them were already on the LT4 treatment for at least 4 months. THs [thyroxin (T4), triiodothyronine (T3), reverse triiodothyronine (rT3), and diiodothyronine (T2)] were estimated. An allele-specific polymerase chain reaction technique was performed to detect the rs1190716; C > T SNP. Results: The genotypes distribution of rs1190716; C > T SNP was 10 (4.5%) for the wild type (CC), 50 (22.7%) for the heterozygous mutant type (TC), and 160 (72.7%) for the homozygous mutant type (TT). The patients were divided into three groups according to their genotypes. Significant differences were found in the T4, T3, and T2 levels among the patients (p=0.019, p=0.039, p=0.032, respectively). Conclusion: The rs1190716; C > T SNP could affect the activity of the D3 enzyme and the metabolic homeostasis of the THs; therefore rs1190716; C > T SNP could have an impact on the therapeutic response to LT4 in Iraqi female patients with primary hypothyroidism. Regarding DIO3 gene, this is a novel finding; hence, further studies are needed to confirm it.

The impaired swim bladder via ROS-mediated inhibition of the Wnt / Hedgehog pathway in zebrafish embryos exposed to eight toxic chemicals and binary chemical mixtures.

To comprehensively explore the potential toxicity of aquatic organisms exposed to chlorinated or brominated flame retardants (BFRs) and metals mixtures, it is necessary to find a common pathway to relate local toxic targeted sites or organs. A key challenge in environmental risk assessment (ERA) is how to clarify the same or different sites or organs of toxic action in a species after exposure to individual chemicals or chemical mixtures. In this study, zebrafish embryo was used to evaluate the sub-lethal toxicity (swim bladder damage) of tris(2,3-dibromo propyl) isocyanurate (TBC), chlorinated paraffins (CPs), hexabromocyclododecane (HBCD), Cu, Cd, Pb, Ag, and Zn through optical microscopy methods, and corresponding sub-lethal molecular levels (inflammation-related enzymes [deiodinase (DIO) enzymes] and transcriptional levels of key genes) in fish through quantitative real-time PCR (qRT-PCR). The tested chemicals all caused failed inflation of the swim bladder, as indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Following embryonic exposure to respective TBC + Cu, HBCD + TBC, and Cd + Pb mixtures, as the concentration of the respective Cu, TBC, and Pb increased, the deformity of the swim bladder increased, as also indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Additionally, eight chemicals down-regulated Wnt (wnt3, wnt9b, fzd3b, wnt1, fzd5, and fdz1) signaling pathways, which were neurotoxic responses to individual chemical treatments and Hedgehog (ihh, shh, ptc1 and ptc2) signaling pathways. Moreover, excessive ROS induced by eight chemicals effectively induced defects in the swim bladder and Wnt/Hedgehog signaling, which also be proved in respective TBC + Cu, HBCD + TBC, and Cd + Pb mixture treatments. Our results first revealed that eight chemicals caused swim bladder developmental defects via ROS-mediated inhibition of the Wnt and Hedgehog pathways, which revealed the common targeted sites or organs (swim bladders) for further studying the toxic mechanisms underlying the chemical mixtures.

Chronic Exposure to Chlorpyrifos Damages Thyroid Activity and Imbalances Hepatic Thyroid Hormones Signaling and Glucose Metabolism: Dependency of T3-FOXO1 Axis by Hyperglycemia.

Early life exposure to Endocrine Disruptor Chemicals (EDCs), such as the organophosphate pesticide Chlorpyrifos (CPF), affects the thyroid activity and dependent process, including the glucose metabolism. The damage of thyroid hormones (THs) as a mechanism of action of CPF is underestimated because the studies rarely consider that TH levels and signaling are customized peripherally. Here, we investigated the impairment of metabolism/signaling of THs and lipid/glucose metabolism in the livers of 6-month-old mice, developmentally and lifelong exposed to 0.1, 1, and 10 mg/kg/die CPF (F1) and their offspring similarly exposed (F2), analyzing the levels of transcripts of the enzymes involved in the metabolism of T3 (Dio1), lipids (Fasn, Acc1), and glucose (G6pase, Pck1). Both processes were altered only in F2 males, affected by hypothyroidism and by a systemic hyperglycemia linked to the activation of gluconeogenesis in mice exposed to 1 and 10 mg/kg/die CPF. Interestingly, we observed an increase in active FOXO1 protein due to a decrease in AKT phosphorylation, despite insulin signaling activation. Experiments in vitro revealed that chronic exposure to CPF affected glucose metabolism via the direct modulation of FOXO1 activity and T3 levels in hepatic cells. In conclusion, we described different sex and intergenerational effects of CPF exposure on the hepatic homeostasis of THs, their signaling, and, finally, glucose metabolism. The data points to FOXO1-T3-glucose signaling as a target of CPF in liver.

Effect of the Fetal THRB Genotype on the Placenta.

CONTEXT: Pregnant women with mutations in the thyroid hormone receptor beta (THRB) gene expose their fetuses to high thyroid hormone (TH) levels shown to be detrimental to a normal fetus (NlFe) but not to an affected fetus (AfFe). However, no information is available about differences in placental TH regulators. OBJECTIVE: To investigate whether there are differences in placentas associated with a NlFe compared with an AfFe, we had the unique opportunity to study placentas from 2 pregnancies of the same woman with THRB mutation G307D. One placenta supported a NlFe while the other an AfFe. METHODS: Sections of placentas were collected and frozen at -80 °C after term delivery of a NlFe and an AfFe. Two placentas from healthy women of similar gestational age were also obtained. The fetal origin of the placental tissues was established by gDNA quantitation of genes on the X and Y chromosomes and THRB gene. Expression and enzymatic activity of deiodinases 2 and 3 were measured. Expression of following genes was also quantitated: MCT10, MCT8, LAT1, LAT2, THRB, THRA. RESULTS: The placenta carrying the AfFe exhibited a significant reduction of deiodinase 2 and 3 activities as well as the expression of the TH transporters MCT10, LAT1 and LAT2, and THRA. CONCLUSION: We present the first study of the effect of the fetal THRB genotype on the placenta. Though limited by virtue of the rarity of THRB mutations and sample availability, we show that the fetal THRB genotype influences the levels of TH regulators in the placenta.

The Physiological Functions and Polymorphisms of Type II Deiodinase.

Type II deiodinase (DIO2) is thought to provide triiodothyronine (T3) to the nucleus to meet intracellular needs by deiodinating the prohormone thyroxine. DIO2 is expressed widely in many tissues and plays an important role in a variety of physiological processes, such as controlling T3 content in developing tissues (e.g., bone, muscles, and skin) and the adult brain, and regulating adaptive thermogenesis in brown adipose tissue (BAT). However, the identification and cloning of DIO2 have been challenging. In recent years, several clinical investigations have focused on the Thr92Ala polymorphism, which is closely correlated with clinical syndromes such as type 2 diabetes, obesity, hypertension, and osteoarthritis. Thr92Ala-DIO2 was also found to be related to bone and neurodegenerative diseases and tumors. However, relatively few reviews have synthesized research on individual deiodinases, especially DIO2, in the past 5 years. This review summarizes current knowledge regarding the physiological functions of DIO2 in thyroid hormone signaling and adaptive thermogenesis in BAT and the brain, as well as the associations between Thr92Ala-DIO2 and bone and neurodegenerative diseases and tumors. This discussion is expected to provide insights into the physiological functions of DIO2 and the clinical syndromes associated with Thr92Ala-DIO2.

Unusual causes of hyperthyrotropinemia and differential diagnosis of primary hypothyroidism: a revised diagnostic flowchart.

The clinical consequences of primary hypothyroidism include cardiovascular morbidity, increased mortality, and poor quality of life; therefore guidelines endorsed by several Scientific Societies recommend measuring circulating thyroid-stimulating hormone (TSH) in patients at risk. The assessment of serum TSH levels is also deemed to be the most robust and accurate biomarker during the management of replacement therapy in patients with a previous diagnosis of primary hypothyroidism. In line with a reflex TSH laboratory strategy, free thyroxine is measured only if the TSH falls outside specific cutoffs, in order to streamline investigations and save unjustified costs. This serum TSH-based approach to both diagnosis and monitoring has been widely accepted by several national and local health services; nevertheless, false-negative or -positive testing may occur, leading to inappropriate management or treatment. This review aims to describe several infrequent causes of increased circulating TSH, including analytical interferences, resistance to TSH, consumptive hypothyroidism, and refractoriness to levothyroxine replacement treatment. We propose a clinical flowchart to aid correct recognition of these various conditions, which represent important potential pitfalls in the diagnosis and treatment of primary hypothyroidism.

Type 2 deiodinase is expressed in anaplastic thyroid carcinoma and its inhibition causes cell senescence.

Anaplastic thyroid cancer (ATC) is a rare thyroid tumor that frequently originates from the dedifferentiation of a well-differentiated papillary or follicular thyroid cancer. Type 2 deiodinase (D2), responsible for the activation of the thyroid hormone thyroxine into tri-iodothyronine (T3), is expressed in normal thyroid cells and its expression is strongly downregulated in papillary thyroid cancer. In skin cancer, D2 has been associated with cancer progression, dedifferentiation, and epithelial-mesenchymal transition. Here, we show that D2 is highly expressed in anaplastic compared to papillary thyroid cancer cell lines and that D2-derived T3 is required for ATC cell proliferation. D2 inhibition is associated with G1 growth arrest and induction of cell senescence, together with reduced cell migration and invasive potential. Finally, we found that mutated p5372R(R248W), frequently found in ATC, is able to induce D2 expression in transfected papillary thyroid cancer cells. Our results show that the action of D2 is crucial for ATC proliferation and invasiveness, providing a potential new therapeutic target for the treatment of ATC.

Deiodinases in thyroid tumorigenesis.

The three deiodinase selenoenzymes are key regulators of intracellular thyroid hormone (TH) levels. The two TH-activating deiodinases (type 1 deiodinase and type 2 deiodinase (D2)) are normally expressed in follicular thyroid cells and contribute to overall TH production. During thyroid tumorigenesis, the deiodinase expression profile changes to customize intracellular TH levels to different requirements of cancer cells. Differentiated thyroid cancers overexpress the TH-inactivating type 3 deiodinase (D3), likely to reduce the TH signaling within the tumor. Strikingly, recent evidence suggests that during the late stage of thyroid tumorigenesis, D2 expression raises and this, together with a reduction in D3 expression levels, increases TH intracellular signaling in dedifferentiated thyroid cancers. These findings call into question the different functions of TH in the various stages of thyroid cancers.

Role of hepatic deiodinases in thyroid hormone homeostasis and liver metabolism, inflammation, and fibrosis.

Thyroid hormones play an essential role in regulating whole-body homeostasis. Deiodinases are known to convert thyroid hormone from the prohormone thyroxine (T4) to the bioactive hormone tri-iodothyronine (T3) and convert both T4 and T3 toward their inactive metabolites 3,3',5'-tri-iodothyronine (rT3) and 3,3'-di-iodothyronine (3,3'-T2). Deiodinases are thus important for the regulation of intracellular thyroid hormone concentrations. This is known to be crucial both during development and adult life in regulating thyroid hormone-related gene transcription. This review discusses the importance of liver deiodinases in determining serum and liver thyroid hormone concentrations, liver metabolism and liver disease.

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism.

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H2O2-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H2O2 as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H2O2 and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

Vandetanib downregulates type 2 deiodinase in fibro/adipogenic progenitors.

Treatment with tyrosine kinase inhibitors (TKIs) has been associated with alterations in circulating thyroid hormone levels, possibly related to perturbations in peripheral thyroid hormone metabolism. In this study, we evaluated the effect of the multi-kinase inhibitor vandetanib on the expression of the three deiodinase selenoenzymes, responsible for the thyroid hormone activation (type 1 and type 2 deiodinases) or for its inactivation (type 3 deiodinase). Here, we show that the multi-kinase inhibitor vandetanib determines a strong cell-specific downregulation of type 2 deiodinase (D2) expression and a significant reduction in D2 enzymatic activity. This occurs in the diffused population of fibro/adipogenic progenitors, which reside in different tissues - including the muscles - and normally express D2. Given the widespread diffusion of mesenchymal cells within the body, our results may explain at least partially the alterations in thyroid hormone levels that occur in vandetanib-treated patients. Our findings represent a step forward into the understanding of the mechanisms by which TKIs induce hypothyroidism and identify a resident cell population in which such an effect takes place.

Thyroid Hormone Metabolism: A Historical Perspective.

In this article, starting with the recognition that iodine is essential for normal thyroid function and is a component of thyroid hormone (TH) molecules, we discuss the many seminal observations and discoveries that have led to identification of various pathways of TH metabolism and their potential roles in TH economy and action. We then recount evidence that TH metabolism participates in maintaining the appropriate content of active hormone in a TH-responsive tissue or cell. Thus, metabolism of the TH is not merely a means by which it is degraded and eliminated from the body, but an essential component of an intricate system by which the thyroid exerts its multiple regulatory effects on almost all organs and tissues. The article ends with a summary of the current concepts and some outstanding questions that are awaiting answers.

In silico insights into the dimer structure and deiodinase activity of type III iodothyronine deiodinase from bioinformatics, molecular dynamics simulations, and QM/MM calculations.

The homodimeric family of iodothyronine deiodinases (Dios) regioselectively remove iodine from thyroid hormones. Currently, structural data has only been reported for the monomer of the mus type III thioredoxin (Trx) fold catalytic domain (Dio3Trx), but the mode of dimerization has not yet been determined. Various groups have proposed dimer structures that are similar to the A-type and B-type dimerization modes of peroxiredoxins. Computational methods are used to compare the sequence of Dio3Trx to related proteins known to form A-type and B-type dimers. Sequence analysis and in silico protein-protein docking methods suggest that Dio3Trx is more consistent with proteins that adopt B-type dimerization. Molecular dynamics (MD) simulations of the refined Dio3Trx dimer constructed using the SymmDock and GalaxyRefineComplex databases indicate stable dimer formation along the ß4α3 interface consistent with other Trx fold B-type dimers. Free energy calculations show that the dimer is stabilized by interdimer interactions between the ß-sheets and α-helices. A comparison of MD simulations of the apo and thyroxine-bound dimers suggests that the active site binding pocket is not affected by dimerization. Determination of the transition state for deiodination of thyroxine from the monomer structure using QM/MM methods provides an activation barrier consistent with previous small model DFT studies.Communicated by Ramaswamy H. Sarma.

Effects of the synthetic progestin levonorgestrel on some aspects of thyroid physiology in common carp (Cyprinus carpio).

The objective of the present study was to assess the effects of levonorgestrel (LNG), a synthetic progestin, on early development and the thyroid system of carp using morphological, histological, immunohistochemical, and gene expression analysis. Fish were exposed to LNG at three levels (3, 31, and 310 ng L-1) from eggs to the onset of juvenile stage (47 days). LNG had no significant effect on early development in common carp or on the occurrence of morphological anomalies. No pathological alterations of the thyroid follicles were found. Immunohistochemical examination of the thyroid follicles using antibodies against thyroxin did not show any differences in fish exposed to 310 ng L-1 LNG compared to the controls. mRNA expression of iodothyronine deiodinases (dio1, 2, 3) was differentially affected by LNG treatment during carp development. Most importantly, dio3 was markedly downregulated in fish exposed to all three LNG levels compared to the controls at the conclusion of the experiment (47 days post-fertilization). A decrease in dio1 or dio3 or an increase in dio2 transcription observed at different time points of the study may be a sign of hypothyroidism. mRNA expression of genes npr, esr1, and esr2b in the body and npr and esr2b in the head of fish exposed to 310 ng L-1 LNG was significantly upregulated compared to the solvent control group at the end of the test. Together, these results show that levonorgestrel caused parallel changes in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-gonad axes.

Selenium-More than Just a Fortuitous Sulfur Substitute in Redox Biology.

Living organisms use selenium mainly in the form of selenocysteine in the active site of oxidoreductases. Here, selenium's unique chemistry is believed to modulate the reaction mechanism and enhance the catalytic efficiency of specific enzymes in ways not achievable with a sulfur-containing cysteine. However, despite the fact that selenium/sulfur have different physicochemical properties, several selenoproteins have fully functional cysteine-containing homologues and some organisms do not use selenocysteine at all. In this review, selected selenocysteine-containing proteins will be discussed to showcase both situations: (i) selenium as an obligatory element for the protein's physiological function, and (ii) selenium presenting no clear advantage over sulfur (functional proteins with either selenium or sulfur). Selenium's physiological roles in antioxidant defence (to maintain cellular redox status/hinder oxidative stress), hormone metabolism, DNA synthesis, and repair (maintain genetic stability) will be also highlighted, as well as selenium's role in human health. Formate dehydrogenases, hydrogenases, glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases will be herein featured.

Modulation of Deiodinase Types 2 and 3 during Skeletal Muscle Regeneration.

The muscle stem-cell niche comprises numerous cell types, which coordinate the regeneration process after injury. Thyroid hormones are one of the main factors that regulate genes linked to skeletal muscle. In this way, deiodinase types 2 and 3 are responsible for the fine-tuning regulation of the local T3 amount. Although their expression and activity have already been identified during muscle regeneration, it is of utmost importance to identify the cell type and temporal pattern of expression after injury to thoroughly comprehend their therapeutic potential. Here, we confirmed the expression of Dio2 and Dio3 in the whole tibialis anterior muscle. We identified, on a single-cell basis, that Dio2 is present in paired box 7 (PAX7)-positive cells starting from day 5 after injury. Dio2 is present in platelet derived growth factor subunit A (PDGFA)-expressing fibro-adipogenic progenitor cells between days 7 and 14 after injury. Dio3 is detected in myogenic differentiation (MYOD)-positive stem cells and in macrophages immediately post injury and thereafter. Interestingly, Dio2 and Dio3 RNA do not appear to be present in the same type of cell throughout the process. These results provide further insight into previously unseen aspects of the crosstalk and synchronized regulation of T3 in injured muscle mediated by deiodinases. The set of findings described here further define the role of deiodinases in muscle repair, shedding light on potential new forms of treatment for sarcopenia and other muscular diseases.

The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats.

PURPOSE: Vitamin A is an essential nutrient with vital biological functions. The present study investigated the effect of different doses of vitamin A palmitate at different time intervals on thyroid hormones and glycemic markers. METHODS: Male rats were administrated vitamin A palmitate at different doses (0, 0.7, 1.5, 3, 6, and 12 mg/kg, oral) and samples were collected at different time intervals of 2, 4, and 6 weeks. The levels of vitamin A, thyroid hormones (T3, T4, and TSH), deiodinases (Dio1 and Dio3), glycemic markers (blood insulin and fasting glucose levels, HOMA IR and HOMA ß), retinol-binding protein 4 (RBP4) and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) were measured. RESULTS: The findings demonstrated that long-term supplementation with high doses of vitamin A palmitate resulted in hypothyroidism (lower T3 and T4 levels and elevated TSH levels) as well as upregulation of Dio1 and Dio3 expression levels. This effect was associated with elevated glucose and insulin levels, enhanced HOMA IR, and decreased HOMA B index. In addition, prolonged vitamin A supplementation significantly increased RBP4 levels that upregulated the expression of PEPCK. CONCLUSION: High doses of vitamin A supplementation increased the risk of hypothyroidism, modulated insulin sensitivity, and over a long period, increased the incidence of type 2 diabetes mellitus associated with oxidative stress and hepatitis.