Thyroid hormone transporters in health and disease.
Jansen Jurgen,Friesema Edith C H,Milici Carmelina,Visser Theo J
Thyroid : official journal of the American Thyroid Association
Cellular entry is required for conversion of thyroid hormone by the intracellular deiodinases and for binding of 3,3',5-triiodothyronine (T(3)) to its nuclear receptors. Recently, several transporters capable of thyroid hormone transport have been identified. Functional expression studies using Xenopus laevis oocytes have demonstrated that organic anion transporters (e.g., OATPs), and L-type amino acid transporters (LATs) facilitate thyroid hormone uptake. Among these, OATP1C1 has a high affinity and specificity for thyroxine (T(4)). OATP1C1 is expressed in capillaries throughout the brain, suggesting it is critical for transport of T(4) over the blood-brain barrier. We have also characterized a member of the monocarboxylate transporter family, MCT8, as a very active and specific thyroid hormone transporter. Human MCT8 shows preference for T(3) as the ligand. MCT8 is highly expressed in liver and brain but is also widely distributed in other tissues. The MCT8 gene is located on the X chromosome. Recently, mutations in MCT8 have been found to be associated with severe X-linked psychomotor retardation and strongly elevated serum T(3) levels.
10.1089/thy.2005.15.757
Mice deficient in MCT8 reveal a mechanism regulating thyroid hormone secretion.
Di Cosmo Caterina,Liao Xiao-Hui,Dumitrescu Alexandra M,Philp Nancy J,Weiss Roy E,Refetoff Samuel
The Journal of clinical investigation
The mechanism of thyroid hormone (TH) secretion from the thyroid gland into blood is unknown. Humans and mice deficient in monocarboxylate transporter 8 (MCT8) have low serum thyroxine (T4) levels that cannot be fully explained by increased deiodination. Here, we have shown that Mct8 is localized at the basolateral membrane of thyrocytes and that the serum TH concentration is reduced in Mct8-KO mice early after being taken off a treatment that almost completely depleted the thyroid gland of TH. Thyroid glands in Mct8-KO mice contained more non-thyroglobulin-associated T4 and triiodothyronine than did those in wild-type mice, independent of deiodination. In addition, depletion of thyroidal TH content was slower during iodine deficiency. After administration of 125I, the rate of both its secretion from the thyroid gland and its appearance in the serum as trichloroacetic acid-precipitable radioactivity was greatly reduced in Mct8-KO mice. Similarly, the secretion of T4 induced by injection of thyrotropin was reduced in Mct8-KO in which endogenous TSH and T4 were suppressed by administration of triiodothyronine. To our knowledge, this study is the first to demonstrate that Mct8 is involved in the secretion of TH from the thyroid gland and contributes, in part, to the low serum T4 level observed in MCT8-deficient patients.
10.1172/JCI42113
Impact of monocarboxylate transporter-8 deficiency on the hypothalamus-pituitary-thyroid axis in mice.
Trajkovic-Arsic Marija,Müller Julia,Darras Veerle M,Groba Claudia,Lee Sooyeon,Weih Debra,Bauer Karl,Visser Theo J,Heuer Heike
Endocrinology
In patients, inactivating mutations in the gene encoding the thyroid hormone-transporting monocarboxylate transporter 8 (Mct8) are associated with severe mental and neurological deficits and disturbed thyroid hormone levels. The latter phenotype characterized by high T3 and low T4 serum concentrations is replicated in Mct8 knockout (ko) mice, indicating that MCT8 deficiency interferes with thyroid hormone production and/or metabolism. Our studies of Mct8 ko mice indeed revealed increased thyroidal T3 and T4 concentrations without overt signs of a hyperactive thyroid gland. However, upon TSH stimulation Mct8 ko mice showed decreased T4 and increased T3 secretion compared with wild-type littermates. Moreover, similar changes in the thyroid hormone secretion pattern were observed in Mct8/Trhr1 double-ko mice, which are characterized by normal serum T3 levels and normal hepatic and renal D1 expression in the presence of very low T4 serum concentrations. These data strongly indicate that absence of Mct8 in the thyroid gland affects thyroid hormone efflux by shifting the ratio of the secreted hormones toward T3. To test this hypothesis, we generated Mct8/Pax8 double-mutant mice, which in addition to Mct8 lack a functional thyroid gland and are therefore completely athyroid. Following the injection of these animals with either T4 or T3, serum analysis revealed T3 concentrations similar to those observed in Pax8 ko mice under thyroid hormone replacement, indicating that indeed increased thyroidal T3 secretion in Mct8 ko mice represents an important pathogenic mechanism leading to the high serum T3 levels.
10.1210/en.2010-0593
IGF-1 receptor deficiency in thyrocytes impairs thyroid hormone secretion and completely inhibits TSH-stimulated goiter.
Ock Sangmi,Ahn Jihyun,Lee Seok Hong,Kang Hyun,Offermanns Stefan,Ahn Hwa Young,Jo Young Suk,Shong Minho,Cho Bo Youn,Jo Daewoong,Abel E Dale,Lee Tae Jin,Park Woo Jin,Lee In-Kyu,Kim Jaetaek
FASEB journal : official publication of the Federation of American Societies for Experimental Biology
Although thyroid-stimulating hormone (TSH) is known to be a major regulator of thyroid hormone biosynthesis and thyroid growth, insulin-like growth factor 1 (IGF-1) is required for mediating thyrocyte growth in concert with TSH in vitro. We generated mice with thyrocyte-selective ablation of IGF-1 receptor (TIGF1RKO) to explore the role of IGF-1 receptor signaling on thyroid function and growth. In 5-wk-old TIGF1RKO mice, serum thyroxine (T4) concentrations were decreased by 30% in concert with a 43% down-regulation of the monocarboxylate transporter 8 (MCT8), which is involved in T4 secretion. Despite a 3.5-fold increase in circulating concentrations of TSH, thyroid architecture and size were normal. Furthermore, thyrocyte area was increased by 40% in WT thyroids after 10 d TSH injection, but this effect was absent in TSH-injected TIGF1RKO mice. WT mice treated with methimazole and sodium perchlorate for 2 or 6 wk exhibited pronounced goiter development (2.0 and 5.4-fold, respectively), but in TIGF1RKO mice, goiter development was completely abrogated. These data reveal an essential role for IGF-1 receptor signaling in the regulation of thyroid function and TSH-stimulated goitrogenesis.
10.1096/fj.13-231381
Tissue-specific alterations in thyroid hormone homeostasis in combined Mct10 and Mct8 deficiency.
Müller Julia,Mayerl Steffen,Visser Theo J,Darras Veerle M,Boelen Anita,Frappart Lucien,Mariotta Luca,Verrey Francois,Heuer Heike
Endocrinology
The monocarboxylate transporter Mct10 (Slc16a10; T-type amino acid transporter) facilitates the cellular transport of thyroid hormone (TH) and shows an overlapping expression with the well-established TH transporter Mct8. Because Mct8 deficiency is associated with distinct tissue-specific alterations in TH transport and metabolism, we speculated that Mct10 inactivation may compromise the tissue-specific TH homeostasis as well. However, analysis of Mct10 knockout (ko) mice revealed normal serum TH levels and tissue TH content in contrast to Mct8 ko mice that are characterized by high serum T3, low serum T4, decreased brain TH content, and increased tissue TH concentrations in the liver, kidneys, and thyroid gland. Surprisingly, mice deficient in both TH transporters (Mct10/Mct8 double knockout [dko] mice) showed normal serum T4 levels in the presence of elevated serum T3, indicating that the additional inactivation of Mct10 partially rescues the phenotype of Mct8 ko mice. As a consequence of the normal serum T4, brain T4 content and hypothalamic TRH expression were found to be normalized in the Mct10/Mct8 dko mice. In contrast, the hyperthyroid situation in liver, kidneys, and thyroid gland of Mct8 ko mice was even more severe in Mct10/Mct8 dko animals, suggesting that in these organs, both transporters contribute to the TH efflux. In summary, our data indicate that Mct10 indeed participates in tissue-specific TH transport and also contributes to the generation of the unusual serum TH profile characteristic for Mct8 deficiency.
10.1210/en.2013-1800
Iodine deficiency up-regulates monocarboxylate transporter 8 expression of mouse thyroid gland.
Hu Zhimei,Zhuo Xiaohua,Shi Yanan,Liu Xin,Yuan Jihong,Li Lanying,Sun Yina
Chinese medical journal
BACKGROUND:Iodine deficiency is a major factor affecting thyroid auto-regulation, the quantity of iodine may greatly influence the synthesis of thyroid hormones (THs). It has long been believed that TH enters the cell through passive diffusion. Recent studies have suggested that several transporters could facilitate transportation of TH. The monocarboxylate transporter 8 (MCT8) was identified as a very active and specific TH transporter. The purpose of this study was to investigate whether iodine insufficient affected the expression of MCT8 in the thyroid gland. METHODS:Sixty BALB/c mice were randomly divided into two groups: control group was fed with standard feed (iodine concentration of 300 µg/kg); while low-iodine (LI) group received iodine-insufficient feed (iodine concentration of 20-40 µg/kg). After 3 months, 10 mice of each group were sacrificed. The remaining 20 mice of each group were kept till 6 months. From the LI group, we randomly selected 15 mice and injected triiodothyronine (T3, 100 µg/kg body weight per day) intraperitoneally for 24, 48 or 72 hours (5 mice for each time-point). Then, all the mice were sacrificed. Mouse serum thyroxine (T4), T3, and thyroid-stimulating hormone (TSH) levels were determined by chemiluminescence immunoassay (CIA). The protein content or messenger RNA (mRNA) level of thyroid MCT8 was measured by Western blotting analysis or real time RT-PCR respectively. MCT8 subcellular location in thyroid tissues was probed with immunohistochemistry (IHC) assay. RESULTS:We found that mouse serum T3 and T4 levels decreased and TSH level increased by the end of the third month. Consistent with these findings, there was significant goiter and hypothyroidism in the LI group. Meanwhile, the MCT8 mRNA increased to 1.36-fold of the level in the control group at the 3(rd) month. At 6(th) month, the serum T4 level in LI mice remained at a lower level, and MCT8 mRNA expression continued rising to nearly 1.60-fold compared with the control group. The protein content was also about 3 times higher than that in the control group. IHC results also revealed MCT8 was of higher expression and localized in the cytoplasm of thyroid follicular cells. After providing exogenous T3 to iodine deficient mice, the serum T3 and T4 gradually increased, whereas MCT8 mRNA and protein both started to decrease and returned to the same level as the control group. CONCLUSION:There is a compensatory increase in thyroid MCT8 expression to enhance its capability to transport TH from thyroid to the blood circulation in iodine deficient mice.
Structure and function of thyroid hormone plasma membrane transporters.
Schweizer Ulrich,Johannes Jörg,Bayer Dorothea,Braun Doreen
European thyroid journal
Thyroid hormones (TH) cross the plasma membrane with the help of transporter proteins. As charged amino acid derivatives, TH cannot simply diffuse across a lipid bilayer membrane, despite their notorious hydrophobicity. The identification of monocarboxylate transporter 8 (MCT8, SLC16A2) as a specific and very active TH transporter paved the way to the finding that mutations in the MCT8 gene cause a syndrome of psychomotor retardation in humans. The purpose of this review is to introduce the current model of transmembrane transport and highlight the diversity of TH transmembrane transporters. The interactions of TH with plasma transfer proteins, T3 receptors, and deiodinase are summarized. It is shown that proteins may bind TH owing to their hydrophobic character in hydrophobic cavities and/or by specific polar interaction with the phenolic hydroxyl, the aminopropionic acid moiety, and by weak polar interactions with the iodine atoms. These findings are compared with our understanding of how TH transporters interact with substrate. The presumed effects of mutations in MCT8 on protein folding and transport function are explained in light of the available homology model.
10.1159/000367858
Thyroid hormone transporters--functions and clinical implications.
Bernal Juan,Guadaño-Ferraz Ana,Morte Beatriz
Nature reviews. Endocrinology
The cellular influx and efflux of thyroid hormones are facilitated by transmembrane protein transporters. Of these transporters, monocarboxylate transporter 8 (MCT8) is the only one specific for the transport of thyroid hormones and some of their derivatives. Mutations in SLC16A2, the gene that encodes MCT8, lead to an X-linked syndrome with severe neurological impairment and altered concentrations of thyroid hormones. Histopathological analysis of brain tissue from patients who have impaired MCT8 function indicates that brain lesions start prenatally, and are most probably the result of cerebral hypothyroidism. A Slc16a2 knockout mouse model has revealed that Mct8 is an important mediator of thyroid hormone transport, especially T3, through the blood-brain barrier. However, unlike humans with an MCT8 deficiency, these mice do not have neurological impairment. One explanation for this discrepancy could be differences in expression of the T4 transporter OATP1C1 in the blood-brain barrier; OATP1C1 is more abundant in rodents than in primates and permits the passage of T4 in the absence of T3 transport, thus preventing full cerebral hypothyroidism. In this Review, we discuss the relevance of thyroid hormone transporters in health and disease, with a particular focus on the pathophysiology of MCT8 mutations.
10.1038/nrendo.2015.66
Follicular thyroglobulin enhances gene expression necessary for thyroid hormone secretion.
Ishido Yuko,Luo Yuqian,Yoshihara Aya,Hayashi Moyuru,Yoshida Akio,Hisatome Ichiro,Suzuki Koichi
Endocrine journal
We have previously shown that follicular thyroglobulin (Tg) has an unexpected function as an autocrine negative-feedback regulator of thyroid hormone (TH) biosynthesis. Tg significantly suppressed the expression of genes necessary for iodide transport and TH synthesis by counteracting stimulation by TSH. However, whether follicular Tg also regulates intracellular TH transport and its secretion from thyrocytes is not known. In the present study, we examined the potential effect of follicular Tg on TH transport and secretion by quantifying the expression of two TH transporters: monocarboxylate transporter 8 (MCT8) and μ-crystallin (CRYM). Our results showed that follicular Tg at physiologic concentrations enhanced both the mRNA and protein expression levels of MCT8 and CRYM in a time- and dose-dependent manner in rat thyroid FRTL-5 cells. Although both the sodium/iodide symporter (NIS), an essential transporter of iodide from blood into the thyroid, and MCT8, a transporter of synthesized TH from the gland, were co-localized on the basolateral membrane of rat thyrocytes in vivo, Tg decreased NIS expression and increased the expression of MCT8 by counteracting TSH action. Thus, the effect of Tg on TH secretion opposed its previously described negative-feedback suppression of TH synthesis. Our results indicate that Tg mediates a complex intrinsic regulation of gene expression that is necessary to balance two opposing vectorial transport systems: the inflow of newly synthesized TH and the outflow of TH by external secretion.
10.1507/endocrj.EJ15-0263
Exposure to2,2',4,4'-tetrabromodiphenyl ether (BDE-47) alters thyroid hormone levels and thyroid hormone-regulated gene transcription in manila clam Ruditapes philippinarum.
Song Ying,Miao Jingjing,Pan Luqing,Wang Xin
Chemosphere
Polybrominated diphenyl ethers (PBDEs) have the potential to disturb the thyroid endocrine system in vertebrates, but little is known about the disruptive effects of PBDEs on marine bivalves. In this study, we first examined the effects of BDE-47 exposure on growth of juvenile manila clams Ruditapes philippinarum. The result showed that 1.0 and 10 μg L(-1) BDE-47 had adverse effects on 14-d shell-length growth of juvenile clams. Then, one-year-old adult clams were exposed to 0, 0.1 and 1 μg L(-1) BDE-47 for 15 d. BDE-47 (1 μg L(-1)) exposure caused significant decreases of total T4 (thyroxine) by 40% and T3 (3,5,3'-triiodothyronine) by 75% concentrations in haemolymph of the clams. Transcription of genes involved in thyroid hormone synthesis and metabolism were also studied by quantitative RT-PCR. Gene expression levels of sodium iodide symporter (rp-NIS), iodothyronine deiodinase (rp-Deio) and thyroid peroxidase (rp-TPO) were increased in a dose-dependent manner at day 5 and day 10, while monocarboxylate transporter 8 (rp-Mct8) was downregulated at day 5, day 10 and day 15. The effect and preliminary mechanism observed in the present study were consistent with the results from previous studies on rodent and fish, implying that exposure to BDE-47 may pose threat to thyroid hormone homeostasis in bivalves through thyroid synthesis and metabolism pathways. This study may provide a first step towards understanding of the thyroid function disruptive effects of PBDEs on marine bivalves and the underlying mechanism across taxonomic groups and phyla.
10.1016/j.chemosphere.2016.02.049
In vitro effects of polychlorinated biphenyls and their hydroxylated metabolites on the synthesis and metabolism of iodothyronines in the chicken (Gallus domesticus) thyroid gland.
Kowalik Kinga,Sechman Andrzej
General and comparative endocrinology
To assess the effect of polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) on thyroid hormone [TH: thyroxine (T) and triiodothyronine (T)] secretion, the concentrations of iodothyronine deiodinases (DIO1, DIO2, DIO3), and mRNA expression of genes involved in TH synthesis (TSHR, NIS, TPO, TG), metabolism (DIO1, DIO2, DIO3), and transport (OATP1C1, MCT8, MCT10, LAT1), chicken thyroid explants were incubated in medium supplemented with TSH (250 mU/ml), PCB118, PCB153, 4-OH-PCB107, and 3-OH-PCB153 (0.5 × 10 M), and TSH together with each PCB and OH-PCB. The results of the in vitro experiment revealed that, except for 4-OH-PCB107, all applied PCBs and OH-PCBs inhibited basal and TSH-stimulated T secretion. Moreover, they increased basal and reduced TSH-stimulated T secretion. PCBs and OH-PCBs decreased the TSH-stimulated TSHR expression. Following PCB and OH-PCB exposure, significant changes in mRNA expression of NIS, TPO, and TG were observed. PCBs and OH-PCBs affected DIO1 and DIO3 transcript levels and protein abundances of each DIO. Furthermore, PCB-dependent effects on OATP1C1, MCT8, and MCT10 mRNA expression were found. In conclusion, both PCB118 and PCB153 and their OH-PCBs affect TH synthesis and deiodination processes in the chicken thyroid gland and influence TH transport across the thyrocyte membrane. In addition, the effects of PCBs and OH-PCBs depended mainly on the type of PCB congener and the exposure time. These results indicate that not only parental PCBs but also OH-PCBs are hazardous for the thyroid gland and may disrupt its endocrine function. Further studies are necessary to explain a mechanism of PCB and OH-PCB action in the avian thyroid gland.
10.1016/j.ygcen.2022.113989
Hydrogen Sulfide Promotes Thyroid Hormone Synthesis and Secretion by Upregulating Sirtuin-1.
Zhao Xue,Cao Yedi,Jin Hongfang,Wang Xiuli,Zhang Lanbo,Zhang Yang,Yu Yang,Huang Youyuan,Gao Ying,Zhang Junqing
Frontiers in pharmacology
One mechanism of hypothyroidism involves the disruption of thyroid hormone synthesis and secretion by thyrocytes. Hydrogen sulfide (HS), as a gas signaling molecule, participates in many physiopathologic processes by upregulating sirtuin-1 (SIRT1). The aim of the current study was to explore whether HS promotes the synthesis and secretion of thyroid hormones by upregulating SIRT1. Real-time PCR and immunohistochemistry were used to detect the mRNA and protein expression of HS-generating enzymes in normal human thyroid tissues. Serum HS concentrations from hypothyroid patients ( = 32) and euthyroid participants ( = 41) were detected by HS-selective sensors. Thirty-one Sprague-Dawley rats were divided into control group ( = 10), hypothyroid group (induced by MMI, = 10) and hypothyroid + NaHS group ( = 11), and the FT4, TT4 and TSH levels were assayed. Human primary thyrocytes were incubated with HS donor sodium hydrosulfide (NaHS) or NaHS plus SIRT1 inhibitor (EX527) . Thyroid hormone synthesis- and secretion-related proteins [thyroid peroxidase (TPO), sodium iodide transporter (NIS), Pendrin, monocarboxylic acid transporter 8 (MCT8)] were analyzed by real-time PCR and Western blot. HS levels in serum from hypothyroid patients were decreased compared to those from euthyroid participants ( < .05), and serum HS levels were positively correlated with FT3, FT4, TT3, and TT4 levels in all subjects (all < .0001). , NaHS promoted thyroid function in hypothyroid rats ( < .05). , HS was detected in supernatant, and mRNA was higher than and in human primary thyrocytes ( < .05). The protein levels of TPO, NIS, Pendrin and MCT8 were upregulated in a concentration-dependent manner for NaHS in thyrocytes. After blocking SIRT1 with EX527, we found that the increasing levels of TPO, NIS, Pendrin, and MCT8 and TPO activity were downregulated in thyrocytes incubated with NaHS, and FT4 levels in the cell supernatant were also decreased significantly (all < .05). HS is mainly generated in thyrocytes by CBS. Serum HS levels are decreased with hypothyroidism. HS promotes the synthesis and secretion of thyroid hormones and the expression of related molecules by upregulating SIRT1.
10.3389/fphar.2022.838248
Altered Expression of Thyroid- and Calcium Ion Channels-Related Genes in Rat Testes by Short-Term Exposure to Commercial Herbicides Paraquat or 2,4-D.
Journal of xenobiotics
Exposure to pesticides such as paraquat and 2,4-dichlorophenoxyacetic acid (2,4-D) has been linked to harmful health effects, including alterations in male reproduction. Both herbicides are widely used in developing countries and have been associated with reproductive alterations, such as disruption of spermatogenesis and steroidogenesis. The thyroid axis and Ca-permeable ion channels play a key role in these processes, and their disruption can lead to reproductive issues and even infertility. This study evaluated the short-term effects of exposure to commercial herbicides based on paraquat and 2,4-D on gene expression in rat testes. At the molecular level, exposure to paraquat increased the expression of the thyroid hormone transporters monocarboxylate transporter 8 () and organic anion-transporting polypeptide 1C1 () and the thyroid receptor alpha (), suggesting a possible endocrine disruption. However, it did not alter the expression of the sperm-associated cation channels () or vanilloid receptor-related osmotically activated channel () related to sperm motility. In contrast, exposure to 2,4-D reduced the expression of the transporter, deiodinase, and , which could affect both the availability of T3 in testicular cells and sperm quality, consistent with previous studies. However, 2,4-D did not affect the expression of or . Deregulation of gene expression could explain the alterations in male reproductive processes reported by exposure to paraquat and 2,4-D. These thyroid hormone-related genes can serve as molecular biomarkers to assess endocrine disruption due to exposure to these herbicides, aiding in evaluating the health risks of pesticides.
10.3390/jox14040081