Thyroid development and effect on the nervous system

Urinary haloacetic acid concentrations and thyroid function among women: Results from the TREE study

BACKGROUND

Disinfection byproducts (DBPs) have been shown to impair thyroid function in experimental models. However, epidemiological evidence is scarce.

METHODS

This study included 1190 women undergoing assisted reproductive technology (ART) treatment from the Tongji Reproductive and Environmental (TREE) cohort from December 2018 to August 2021. Serum thyrotropin (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were measured as indicators of thyroid function. FT4/FT3 and TSH/FT4 ratios were calculated as markers of thyroid hormone homeostasis. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two most abundant HAAs, in urine were detected to assess individual DBP exposures.

RESULTS

After adjusting for relevant covariates, positive associations were observed between urinary TCAA concentrations and serum TSH and TSH/FT4 levels (e.g., percent change = 5.82 %, 95 % CI: 0.70 %, 11.21 % for TSH), whereas inverse associations were found for serum FT3 and FT4 (e.g., percent change = -1.29 %, 95 % CI: -2.49 %, -0.07 % for FT3). There also was a negative association between urinary DCAA concentration and serum FT4/FT3 (percent change = -2.49 %, 95 % CI: -4.71 %, -0.23 %). These associations were further confirmed in the restricted cubic spline and generalized additive models with linear or U-shaped dose-response relationships.

CONCLUSION

Urinary HAAs were associated with altered thyroid hormone homeostasis among women undergoing ART treatment.

Elimination of the color discrimination impairment along the blue-yellow axis in patients with hypothyroidism after treatment with levothyroxine as assessed by the Farnsworth-Munsell 100 hue test

Our previous study has shown that individuals with untreated hypothyroidism display significantly higher partial error scores (P E S) along the blue-yellow axis compared to the red-green axis than normal individuals using the Farnsworth-Munsell 100 hue test [J. Opt. Soc. Am. A37, A18 (2020)JOAOD60740-323210.1364/JOSAA.382390]. We wished to determine how color discrimination may change when hypothyroidism has been treated to the point of euthyroidism. Color discrimination was reassessed for 17 female individuals who had undergone treatment for hypothyroidism, and the results were compared with 22 female individuals without thyroid dysfunction. No statistically significant difference was found in the total error score (T E S) for the first and second measurements for both groups (p>0.45). The P E S for the hypothyroid group improved significantly in the previously impaired color regions after the treatment. Color discrimination defects found in untreated hypothyroidism can be negated with treatment of the condition over an appropriate time period.

Pathophysiology and Management Possibilities of Thyroid-Associated Depression

Thyroid hormones and the hypothalamic-pituitary-thyroid (HPA) axis are responsible for multiple metabolic processes and psychological well-being. Hypothyroidism can induce mood changes, depressive symptoms and even major depressive disorder. This review is focused on the pathophysiology and mechanisms through which the low level of thyroid hormones may affect the brain function, causing the characteristic symptoms of depression. Key pathways of hypothyroid-associated depressive states include: morphological changes in some brain areas (mainly in the hippocampus – a reduction in its volume); a significant reduction of the cerebral blood flow (incl. hippocampus), and lowered levels of neurotrophic factors (e. g. BDNF – brain-derived neurotrophic factor), which are regulated by the thyroid hormones. An adequate and timely thyroid hormone replacement and treatment with conventional antidepressants often can reverse the psychological symptoms.

Şizofreni hastalarında TSH, fT3 ve fT4 düzeylerinin nörobilişsel belirtiler üzerine etkisi

Amaç: Bu çalışmamızda ötiroid psikoz hastalarında tiroid hormon düzeyleri ile pozitif, negatif, genel ve bilişsel belirtiler arasındaki ilişkiyi incelemeyi amaçladık. Gereç ve Yöntem: Çalışmaya 33 şizofreni hastası dahil edildi. Katılımcıların sosyodemografik ve klinik verileri, Pozitif ve Negatif Belirtileri Değerlendirme Ölçeği (PANSS), İşlevselliğin Genel Değerlendirilmesi Ölçeği (IGD), Klinik Global İzlenim Ölçeği (KGI) skorları kaydedildi. İz sürme, Sözel Akıcılık Testi, İleri ve Geri Sayı Menzili ile Wisconsin Kart Sayma Testinden (WKST) oluşan bir nörobilişsel batarya uygulanan hastaların bilişsel performanslarının TSH, sT3 ve sT4 düzeyleri ile ilişkisi araştırıldı. Bulgular: sT4 düzeyleri ile İz Sürme B (r=-,376; p=0,031) ve Sözel Akıcılık test (p=,355; p=0,043) performansları arasında anlamlı derecede ilişki saptandı. Linear regresyon modelinde sT3 düzeylerinin WKST- tamamlanan kategori sayısını (UB=1.680; p=0.029) anlamlı derecede yordadığı saptandı.. Sonuç: Çalışmamızın sonuçları sT3 ün özellikle yürütücü işlevler üzerinde sT4’e kıyasla daha belirleyici etkileri olduğunu düşündürmüştür. İleride yapılacak daha geniş katılımlı araştırmalar, bilişsel belirtilerin tedavisinde tiroid hormon replasmanının etkinliğini belirlemek açısından önemli görünmektedir.

Zebrafish as an emerging tool for drug discovery and development for thyroid diseases

Zebrafish is a useful model for understanding human genetics and diseases and has evolved into a prominent scientific research model. The genetic structure of zebrafish is 70% identical to that of humans. Its small size, low cost, and transparent embryo make it a valuable tool in experimentation. Zebrafish and mammals possess the same molecular mechanism of thyroid organogenesis and development. Thus, thyroid hormone signaling, embryonic development, thyroid-related disorders, and novel genes involved in early thyroid development can all be studied using zebrafish as a model. Here in this review, we emphasize the evolving role of zebrafish as a possible tool for studying the thyroid gland in the context of physiology and pathology. The transcription factors nkx2.1a, pax2a, and hhex which contribute a pivotal role in the differentiation of thyroid primordium are discussed. Further, we have described the role of zebrafish as a model for thyroid cancer, evaluation of defects in thyroid hormone transport, thyroid hormone (TH) metabolism, and as a screening tool to study thyrotoxins. Hence, the present review highlights the role of zebrafish as a novel approach to understand thyroid development and organogenesis.

Histological, functional and transcriptomic alterations in the juvenile hippocampus in a mouse model of thyroid hormone resistance

BACKGROUND

Proper thyroid hormone signaling via the TRα1 nuclear receptor is required for normal neurodevelopmental processes. The specific downstream mechanisms mediated by TRα1 that impact brain development remain to be investigated.

METHODS

In this study, the structure, function and transcriptome of hippocampal tissue in a mouse model expressing the first RTHα mutation discovered in a patient, THRA E403X, were analyzed. RNAscope was used to visualize the spatial and temporal expression of Thra1 mRNA in the hippocampus of WT mice, which is corresponding to THRA1 mRNA in humans. The morphological structure was analyzed by Nissl staining, and the synaptic transmission was analyzed on the basis of long-term potentiation. The Morris water maze test and the zero maze test were used to evaluate the behavior. RNA-seq and quantitative real-time PCR were used to analyze the differentially expressed genes (DEGs) of the hippocampal tissues in the mouse model expressing the Thra E403X mutation.

RESULTS

The juvenile mutant Thra E403X mice presented with delayed neuronal migration, disordered neuronal distribution, and decreased synaptic plasticity. A total of 754 DEGs, including 361 upregulated genes and 393 downregulated genes, were identified by RNA-seq. DEG-enriched Gene Ontology (GO) and KEGG pathways were associated with PI3K-Akt signaling, ECM-receptor interaction, neuroactive ligand-receptor interaction, and a range of immune-related pathways. 25 DEGs were validated by qPCR.

CONCLUSIONS

The ThraE403X mutation results in histological and functional abnormalities, as well as transcriptomic alterations in the juvenile mouse hippocampus. This study of the ThraE403X mutant offers new insights into the biological cause of RTHα-associated neurological diseases.

Developmental Hypothyroidism Influences the Development of the Entorhinal-Dentate Gyrus Pathway of Rat Offspring

BACKGROUND

Developmental hypothyroidism impairs learning and memory in offspring, which depend on extensive neuronal circuits in the entorhinal cortex, together with the hippocampus and neocortex. The entorhinal-dentate gyrus pathway is the main entrance of memory circuits. We investigated whether developmental hypothyroidism impaired the morphological development of the entorhinal-dentate gyrus pathway.

METHODS

We examined the structure and function of the entorhinal-dentate gyrus pathway in response to developmental hypothyroidism induced using 2-mercapto-1-methylimidazole.

RESULTS

1,1´-Dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate tract tracing indicated that entorhinal axons showed delayed growth in reaching the outer molecular layer of the dentate gyrus at postnatal days 2 and 4 in hypothyroid conditions. The proportion of fibers in the outer molecular layer was significantly smaller in the hypothyroid group than in the euthyroid group at postnatal day 4. At postnatal day 10, the pathway showed a layer-specific distribution in the outer molecular layer, similar to the euthyroid group. However, the projected area of entorhinal axons was smaller in the hypothyroid group than in the euthyroid group. An electrophysiological examination showed that hypothyroidism impaired the long-term potentiation of the perforant and the cornu ammonis 3-cornu ammonis 1 pathways. Many repulsive axon guidance molecules were involved in the formation of the entorhinaldentate gyrus pathway. The hypothyroid group had higher levels of erythropoietin-producing hepatocyte ligand A3 and semaphorin 3A than the euthyroid group.

CONCLUSION

We demonstrated that developmental hypothyroidism might influence the development of the entorhinal-dentate gyrus pathway, contributing to impaired long-term potentiation. These findings improve our understanding of neural mechanisms for memory function.

Perchlorate, nitrate, and thiocyanate: Environmental relevant NIS-inhibitors pollutants and their impact on thyroid function and human health

Thyroid disruptors are found in food, atmosphere, soil, and water. These contaminants interfere with the thyroid function through the impairment of thyroid hormone synthesis, plasma transport, peripheral metabolism, transport into the target cells, and thyroid hormone action. It is well known that iodide uptake mediated by the sodium-iodide symporter (NIS) is the first limiting step involved in thyroid hormones production. Therefore, it has been described that several thyroid disruptors interfere with the thyroid function through the regulation of NIS expression and/or activity. Perchlorate, nitrate, and thiocyanate competitively inhibit the NIS-mediated iodide uptake. These contaminants are mainly found in food, water and in the smoke of cigarettes. Although the impact of the human exposure to these anions is highly controversial, some studies indicated their deleterious effects in the thyroid function, especially in individuals living in iodine deficient areas. Considering the critical role of thyroid function and the production of thyroid hormones for growth, metabolism, and development, this review summarizes the impact of the exposure to these NIS-inhibitors on thyroid function and their consequences for human health.

Color discrimination assessment in patients with hypothyroidism using the Farnsworth-Munsell 100 hue test

There is evidence in the literature that hypofunction of the thyroid gland (hypothyroidism) affects color vision in rodents by influencing the production of the visual pigment opsin. The effect of hypothyroidism on color vision in humans has not been examined in any great detail. In this cross-sectional study we evaluated color discrimination using the Farnsworth-Munsell 100 hue test (FM-100 test) in 25 individuals with pre-treatment hypothyroidism (mean age ${38}\;{\pm }\;{9}.{2}\;\text{yr}$38±9.2yr), and a control euthyroid group, ${ n} ={26}$n=26 (mean age ${39.6}\;{\pm }\;{8}.{4}\;\text{yr}$39.6±8.4yr). There was no statistically significant difference in the total error score ($\surd{\text{TES}}$√TES) between the groups, but the hypothyroid group had a significantly greater partial error score ($\surd{\text{PES}}$√PES) along the blue-yellow (B-Y) axis compared to the red-green (R-G) axis. No statistically significant differences in B-Y and R-G PES were observed in the control group. This study shows that hypothyroidism affects color vision in humans, causing significant impairment in the B-Y color subsystem.

Expanding the phenotypic spectrum of Allan-Herndon-Dudley syndrome in patients with SLC16A2 mutations

The aim of the study was to redefine the phenotype of Allan-Herndon-Dudley syndrome (AHDS), which is caused by mutations in the SLC16A2 gene that encodes the brain transporter of thyroid hormones. Clinical phenotypes, brain imaging, thyroid hormone profiles, and genetic data were compared to the existing literature. Twenty-four males aged 11 months to 29 years had a mutation in SLC16A2, including 12 novel mutations and five previously described mutations. Sixteen patients presented with profound developmental delay, three had severe intellectual disability with poor language and walking with an aid, four had moderate intellectual disability with language and walking abilities, and one had mild intellectual disability with hypotonia. Overall, eight had learned to walk, all had hypotonia, 17 had spasticity, 18 had dystonia, 12 had choreoathetosis, 19 had hypomyelination, and 10 had brain atrophy. Kyphoscoliosis (n=12), seizures (n=7), and pneumopathies (n=5) were the most severe complications. This study extends the phenotypic spectrum of AHDS to a mild intellectual disability with hypotonia. Developmental delay, hypotonia, hypomyelination, and thyroid hormone profile help to diagnose patients. Clinical course depends on initial severity, with stable acquisition after infancy; this may be adversely affected by neuro-orthopaedic, pulmonary, and epileptic complications. WHAT THIS PAPER ADDS: Mild intellectual disability is associated with SLC16A2 mutations. A thyroid hormone profile with a free T₃ /T₄ ratio higher than 0.75 can help diagnose patients. Patients with SLC16A2 mutations present a broad spectrum of neurological phenotypes that are also observed in other hypomyelinating disorders. Axial hypotonia is a consistent feature of Allan-Herndon-Dudley syndrome and leads to specific complications.

The effects of thyroid hormones on memory impairment and Alzheimer's disease

Thyroid hormones (THs) have a wide and important range of effects within the central nervous system beginning from fetal life and continuing throughout the adult life. Thyroid disorders are one of the major causes of cognitive impairment including Alzheimer's disease (AD). Several studies in recent years have indicated an association between hypothyroidism or hyperthyroidism and AD. Despite available evidence for this association, it remains unclear whether thyroid dysfunction results from or contributes to the progression of AD. This review discusses the role of THs in learning and memory and summarizes the studies that have linked thyroid function and AD. Eventually, we elaborate how THs may be effective in treating AD by putting forward potential mechanisms.

Therapy with propylthiouracil for T3-predominant neonatal Graves' disease: a case report

This case report describes a male neonate with Graves’ disease. The mother’s pregnancy was complicated by poorly controlled Graves’ disease. The neonate was diagnosed with thyroxine (T3)-predominant Graves’ disease with low free triiodothyronine (T4) and high free T3 during antithyroid drug therapy. The patient also presented with persistent pulmonary hypertension of the newborn due to hyperthyroidism and airway stenosis caused by goiter. It was difficult to control thyroid function and maintain free T4 levels with inorganic iodine, thiamazole, and levothyroxine sodium hydrate. We successfully controlled thyroid function using the previous treatments in combination with propylthiouracil. Propylthiouracil suppresses type 1 iodothyronine deiodinase, and its pharmacological action suppresses the conversion of T4 to T3. Therefore, we used propylthiouracil at an earlier stage of intervention in this case. We ceased administration of antithyroid drugs on day 85 of life. Subsequently, as the TRH loading test revealed central hypothyroidism, oral administration of levothyroxine sodium hydrate was continued. Its administration was discontinued at the age of 1 yr. Thyroid-stimulating hormone recovered to normal values, and his development had progressed without complications by the age of 2 yr.

Regulation of T3 Availability in the Developing Brain: The Mouse Genetics Contribution

Alterations in maternal thyroid physiology may have deleterious consequences on the development of the fetal brain, but the underlying mechanisms remain elusive, hampering the development of appropriate therapeutic strategies. The present review sums up the contribution of genetically modified mouse models to this field. In particular, knocking out genes involved in thyroid hormone (TH) deiodination, transport, and storage has significantly improved the picture that we have of the economy of TH in the fetal brain and the underlying genetic program. These data pave the way for future studies to bridge the gap in knowledge between thyroid physiology and brain development.

Contribution of Brain Tissue Oxidative Damage in Hypothyroidism-associated Learning and Memory Impairments

The brain is a critical target organ for thyroid hormones, and modifications in memory and cognition happen with thyroid dysfunction. The exact mechanisms underlying learning and memory impairments due to hypothyroidism have not been understood yet. Therefore, this review was aimed to compress the results of previous studies which have examined the contribution of brain tissues oxidative damage in hypothyroidism-associated learning and memory impairments.

Neuronal expression of a thyroid hormone receptor α mutation alters mouse behaviour

In humans, alterations in thyroid hormone signalling are associated with mood and anxiety disorders, but the neural mechanisms underlying such association are poorly understood. The present study investigates the involvement of neuronal thyroid hormone receptor α (TRα) in anxiety, using mouse genetics and Cre/loxP technology to specifically alter TRα signalling in neurons. We evaluated the behaviour of mice expressing a dominant negative, neuron-specific mutation of TRα (TRα^AMI/Cre3 mice), using the elevated-plus maze, light-dark box and open-field tests. In a first experiment, mice were housed individually, and the behaviour of TRα^AMI/Cre3 mice differed significantly from that of control littermates in these 3 tests, suggesting heightened anxiety. In a second experiment, designed to evaluate the robustness of the results with the same 3 tests, mice were housed in groups. In these conditions, the behaviour of TRα^AMI/Cre3 mice differed from that of control littermates only in the light-dark box. Thus, TRα^AMI/Cre3 mice appear to be more likely to develop anxiety under stressful housing conditions than control mice. These results suggest that in adult mice, thyroid hormone signalling in neurons, via TRα, is involved in the control of anxiety behaviour.

Depressive symptoms, thyroid hormone and autoimmunity in a population-based cohort from Sardinia

OBJECTIVE

To evaluate the association between depressive symptoms and thyroid autoimmunity, and the effect of thyroid hormone on the risk of depression.

METHODS

We included 3138 individuals from SardiNIA project, none of whom was taking thyroid medication and antidepressants. Thyrotropin (TSH), free thyroxine (FT4), and antibodies against thyroperoxidase (TPOAb) were measured in all the sample. Depressive symptoms were assessed with Center for Epidemiologic Studies Depression Scale (CES-D).

RESULTS

We found no association between TPOAb and depressive symptoms and no linear association between TSH or FT4 levels and depressive symptoms. However, individuals in the lowest and highest FT4 quintiles showed a higher CES-D score compared to individuals in the middle quintile. In addition, participants in the lowest and highest FT4 quintiles had an increased risk of CES-D≥16 with odds ratios of 1.44 (95% CI=1.09-1.89) and 1.33 (95% CI=1.01-1.77), respectively.

LIMITATIONS

Cross-sectional design of the study.

CONCLUSIONS

A U-shaped relation was found between FT4 and depressive symptoms: compared to average FT4 values, both high and low thyroid function was associated with more depressive symptoms. Further studies are necessary to determine the exact cause-effect relation of this association.

Neurophysiologic evaluation of infants with congenital hypothyroidism before and after treatment

We performed a systematic neurophysiological evaluation of newborns-infants newly diagnosed with congenital hypothyroidism and started on replacement therapy, in order to document the maturation of visual, auditory and somesthetic pathways and to evaluate the influence of treatment. Twenty-one patients (9 boys, 12 girls) were studied. They underwent neurophysiological evaluation consisting of visual, auditory, and somatosensory evoked potentials at diagnosis, as well as 6 and 12 months after initiation of treatment. At the time of diagnosis, 47.61 % of the patients had abnormal evoked potentials, with visual evoked potentials being most commonly abnormal. Twelve months after the onset of treatment, abnormal evoked potentials were detected in 33.3 % of the patients. In newly diagnosed infants with congenital hypothyroidism there is a high relevance of abnormal evoked potentials (47.61 %) at the time of diagnosis, declining with time and not correlating with the severity of the disease at diagnosis, the time of diagnosis or the initial dose of thyroxine.

Upregulation of inorganic pyrophosphatase 1 as a JNK phosphatase in hypothyroid embryonic chick cerebellum

AIM

Thyroid hormones play important roles in vertebrate neuronal development and differentiation. In our previous study, we showed that fetal thyroid dysfunction led to impaired social behaviors of hatchlings on post-hatch day 3, as well as to impaired learning and memory determined by the imprinting preference. However, little is known about the mechanisms underlying the direct adverse effects of fetal thyroid dysfunction on neuronal development.

MATERIALS AND METHODS

We used a chick embryo as a fetal model to investigate the effects of prenatal exposure to antithyroid drugs on neuronal development in the chick cerebellum. Methimazole (MMI) at a dose of 20μmol/egg was administered to eggs on day 14, while the control was given only a vehicle. In order to address the underlying mechanisms of the impaired behavior, proteomic approaches were employed in the chick cerebellum two days after MMI treatment.

KEY FINDINGS

In this experiment, we found that inorganic pyrophosphatase 1 (PPA1) was upregulated in the chick cerebellum treated with MMI, and we confirmed this upregulation of PPA1 by Western blot analysis as well as by RT-PCR analysis. Concomitant with the upregulation of PPA1, a marked reduction in JNK activity, as well as of phospho-JNK level, was detected in the MMI-treated chick cerebellum.

SIGNIFICANCE

Since PPA1 can dephosphorylate JNK, these results suggest that the upregulation of PPA1 during neuronal development in the hypothyroid chick cerebellum may lead to impaired social behaviors as well as to impaired learning and memory via JNK dephosphorylation and inactivation in the chick cerebellum.

Thyroid transcription factors in development, differentiation and disease

Identification of the thyroid transcription factors (TTFs), NKX2-1, FOXE1, PAX8 and HHEX, has considerably advanced our understanding of thyroid development, congenital thyroid disorders and thyroid cancer. The TTFs are fundamental to proper formation of the thyroid gland and for maintaining the functional differentiated state of the adult thyroid; however, they are not individually required for precursor cell commitment to a thyroid fate. Although knowledge of the mechanisms involved in thyroid development has increased, the full complement of genes involved in thyroid gland specification and the signals that trigger expression of the genes that encode the TTFs remain unknown. The mechanisms involved in thyroid organogenesis and differentiation have provided clues to identifying the genes that are involved in human congenital thyroid disorders and thyroid cancer. Mutations in the genes that encode the TTFs, as well as polymorphisms and epigenetic modifications, have been associated with thyroid pathologies. Here, we summarize the roles of the TTFs in thyroid development and the mechanisms by which they regulate expression of the genes involved in thyroid differentiation. We also address the implications of mutations in TTFs in thyroid diseases and in diseases not related to the thyroid gland.

Thyroid hormones and their nuclear receptors: new players in intestinal epithelium stem cell biology?

Thyroid hormones participate in the development and homeostasis of several organs and tissues. It is well documented that they act via nuclear receptors, the TRs, which are transcription factors whose function is modulated by the hormone T3. Importantly, T3-induced physiological response within a cell depends on the specific TR expression and on the T3 bioavailability. However, in addition to this T3-dependent control of TR functionality, increasing data show that the action of TRs is coordinated and integrated with other signaling pathways, specifically at the level of stem/progenitor cell populations. By focusing on the intestinal epithelium of both amphibians and mammals we summarize here new data in support of a role for thyroid hormones and the TR nuclear receptors in stem cell biology. This new concept may be extended to other organs and have biological relevance in therapeutic approaches aimed to target stem cells such as tissue engineering and cancer.

Knockdown of monocarboxylate transporter 8 (mct8) disturbs brain development and locomotion in zebrafish

Allan-Herndon-Dudley syndrome (AHDS) is an inherited disorder of brain development characterized by severe psychomotor retardation. This X-linked disease is caused by mutations in the monocarboxylate transporter 8 (MCT8), an important thyroid hormone transporter in brain neurons. MCT8-knockout mice lack the 2 major neurological symptoms of AHDS, namely locomotor problems and cognitive impairment. The pathological mechanism explaining the symptoms is still obscure, and no cure for this condition is known. The development of an animal model that carries MCT8-related neurological symptoms is warranted. We have employed morpholino-based gene knockdown to create zebrafish deficient for mct8. Knockdown of mct8 results in specific symptoms in the thyroid axis and brain. The mct8-morphants showed impaired locomotor behavior and brain development. More specifically, we observed maldevelopment of the cerebellum and mid-hindbrain boundary and apoptotic clusters in the zebrafish brain. The mRNA expression of zebrafish orthologs of mammalian TSH, thyroid hormone transporters, and deiodinases was altered in mct8 morphants. In particular, deiodinase type 3 gene expression was consistently up-regulated in zebrafish mct8 morphants. The thyroid hormone metabolite tetrac, but not T3, partly ameliorated the affected phenotype and locomotion disability of morphant larvae. Our results show that mct8 knockdown in zebrafish larvae results in disturbances in the thyroid axis, brain, and locomotion behavior, which is congruent with the clinical aspect of impaired locomotion and cognition in patients with AHDS. Taken together, the zebrafish is a suitable animal model for the study of the pathophysiology of AHDS.

Thyroid hormone treated astrocytes induce maturation of cerebral cortical neurons through modulation of proteoglycan levels

Proper brain neuronal circuitry formation and synapse development is dependent on specific cues, either genetic or epigenetic, provided by the surrounding neural environment. Within these signals, thyroid hormones (T3 and T4) play crucial role in several steps of brain morphogenesis including proliferation of progenitor cells, neuronal differentiation, maturation, migration, and synapse formation. The lack of thyroid hormones during childhood is associated with several impair neuronal connections, cognitive deficits, and mental disorders. Many of the thyroid hormones effects are mediated by astrocytes, although the mechanisms underlying these events are still unknown. In this work, we investigated the effect of 3, 5, 3′-triiodothyronine-treated (T3-treated) astrocytes on cerebral cortex neuronal differentiation. Culture of neural progenitors from embryonic cerebral cortex mice onto T3-treated astrocyte monolayers yielded an increment in neuronal population, followed by enhancement of neuronal maturation, arborization and neurite outgrowth. In addition, real time PCR assays revealed an increase in the levels of the heparan sulfate proteoglycans, Glypican 1 (GPC-1) and Syndecans 3 e 4 (SDC-3 e SDC-4), followed by a decrease in the levels of the chondroitin sulfate proteoglycan, Versican. Disruption of glycosaminoglycan chains by chondroitinase AC or heparanase III completely abolished the effects of T3-treated astrocytes on neuronal morphogenesis. Our work provides evidence that astrocytes are key mediators of T3 actions on cerebral cortex neuronal development and identified potential molecules and pathways involved in neurite extension; which might eventually contribute to a better understanding of axonal regeneration, synapse formation, and neuronal circuitry recover.

Effects of complex organohalogen contaminant mixtures on thyroid homeostasis in hooded seal (Cystophora cristata) mother-pup pairs

Many lipid-soluble and phenolic compounds present in the complex mixture of orgaohalogen contaminants (OHCs) that arctic wildlife is exposed to have the ability to interfere with the thyroid hormone (TH) system. The aim of this study was to identify compounds that might interfere with thyroid homeostasis in 14 nursing hooded seal (Cystophora cristata) mothers and their pups (1-4d old) sampled in the West Ice in March 2008. Multivariate modelling was used to assess the potential effects of measured plasma levels of OHCs on circulating TH levels of the measured free (F) and total (T) levels of triidothyrine (T3) and thyroxine (T4). Biological factors were important in all models (e.g. age and sex). In both mothers and pups, TT3:FT3 ratios were associated with α- and β-hexachlorocyclohexane (HCH), ortho-PCBs, chlordanes and DDTs. The similarities between the modelled TT3:FT3 responses to OHC levels in hooded seal mothers and pups most probably reflects similar exposure patterns, but could also indicate interconnected TH responses. There were some differences in the modelled TH responses of mothers and pups. Most importantly, the negative relationships between many OH-PCBs (particularly 3'-OH-CB138) and TT3:FT3 ratio and the positive relationships between TT4:FT4 ratios and polybrominated diphenyl ether [PBDE]-99, -100 and 4-OH-CB107 in pups, which was not found in mothers. Although statistical associations are not evidence per se of biological cause-effect relationships, the results suggest that thyroid homeostasis is affected in hooded seals, and that the inclusion of the fullest possible OHC mixture is important when assessing TH related effects in wildlife.

Maternal thyroid dysfunction and risk of seizure in the child: a Danish nationwide cohort study

Thyroid hormones are essential for brain development, and maternal thyroid disease may affect child neurocognitive development. Some types of seizures may also depend upon early exposure of the developing central nervous system, and we hypothesized that maternal thyroid dysfunction could increase the risk of seizure in the child. In a Danish population-based study we included 1,699,693 liveborn singletons, and from the Danish National Hospital Register we obtained information on maternal diagnosis of hyper- or hypothyroidism and neonatal seizure, febrile seizure, and epilepsy in the child. Maternal diagnosis of thyroid dysfunction before or after birth of the child was registered in two percent of the singleton births. In adjusted analyses, maternal hyperthyroidism and hypothyroidism first time diagnosed after birth of the child were associated with a significant increased risk of epilepsy in the child. Moreover, hypothyroidism diagnosed after birth of the child was associated with a significant increased risk of neonatal and febrile seizures. No significant association was seen for maternal diagnosis prior to birth of the child. We speculate if some degree of maternal thyroid dysfunction was already present during the pregnancy in mothers diagnosed after birth of the child and if this untreated condition may present a neurodevelopmental risk.

Clinical phenotype of a new type of thyroid hormone resistance caused by a mutation of the TRα1 receptor: consequences of LT4 treatment

CONTEXT

Recently the first patients with inactivating mutations in T₃ receptor (TR)-α1 have been identified. These patients have low free T₄, low T₄, high T₃, low rT₃, and normal TSH serum levels, in combination with growth retardation, delayed bone development, and constipation.

OBJECTIVE

The aim of the current study was to report the effects of levothyroxine (LT4) treatment on the clinical phenotype of 2 patients (father and daughter) with a heterozygous inactivating mutation in TRα1.

SETTING AND PARTICIPANTS

Both patients were treated with LT4 for the last 5 years. To evaluate the effect of LT4 treatment, LT4 was withdrawn for 35 days and subsequently reinitiated. Data were collected from medical records, by reanalysis of serum collected over the last 6 years, and by a detailed clinical evaluation.

RESULTS

Treatment with LT4 resulted in a suppression of serum TSH and normalization of serum free T₄ and rT₃, whereas T₃ levels remained elevated in both patients. In addition, there was a normalization of the dyslipidemia as well as a response in serum IGF-I, SHBG, and creatine kinase in the index patient. All these parameters returned to pretreatment values when LT4 was briefly stopped. LT4 also resulted in an improvement of certain clinical features, such as constipation and nerve conductance. However, cognitive and fine motor skill defects remained.

CONCLUSION

This study reports the consequences of LT4 treatment over a prolonged period of time in 2 of the first patients with a heterozygous mutation in TRα1. LT4 therapy leads to an improvement of certain but not all features of the clinical phenotype.

Mutations in MCT8 in patients with Allan-Herndon-Dudley-syndrome affecting its cellular distribution

Monocarboxylate transporter 8 (MCT8) is a thyroid hormone (TH)-specific transporter. Mutations in the MCT8 gene are associated with Allan-Herndon-Dudley Syndrome (AHDS), consisting of severe psychomotor retardation and disturbed TH parameters. To study the functional consequences of different MCT8 mutations in detail, we combined functional analysis in different cell types with live-cell imaging of the cellular distribution of seven mutations that we identified in patients with AHDS. We used two cell models to study the mutations in vitro: 1) transiently transfected COS1 and JEG3 cells, and 2) stably transfected Flp-in 293 cells expressing a MCT8-cyan fluorescent protein construct. All seven mutants were expressed at the protein level and showed a defect in T3 and T4 transport in uptake and metabolism studies. Three mutants (G282C, P537L, and G558D) had residual uptake activity in Flp-in 293 and COS1 cells, but not in JEG3 cells. Four mutants (G221R, P321L, D453V, P537L) were expressed at the plasma membrane. The mobility in the plasma membrane of P537L was similar to WT, but the mobility of P321L was altered. The other mutants studied (insV236, G282C, G558D) were predominantly localized in the endoplasmic reticulum. In essence, loss of function by MCT8 mutations can be divided in two groups: mutations that result in partial or complete loss of transport activity (G221R, P321L, D453V, P537L) and mutations that mainly disturb protein expression and trafficking (insV236, G282C, G558D). The cell type-dependent results suggest that MCT8 mutations in AHDS patients may have tissue-specific effects on TH transport probably caused by tissue-specific expression of yet unknown MCT8-interacting proteins.

Effects of polybrominated diphenyl ethers on thyroid hormone, neurodevelopment and fertility in rodents and humans

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants. Due to their widespread use in many consumer products, PBDEs can be found in food as well as in the environment. Their presence has also been found in the human serum, human adipose tissue and human breast milk. Results of experimental studies suggest that the presence of PBDE in the environment is not neutral to our health. In rats and mice exposed to PBDE disturbances in thyroid hormone homeostasis and reproductive system such as changes in reproductive organs weight and disorders in sperm motility and motion were found. In rodents, pre- and postnatal exposure to PBDE can cause neurobehavioral effects. Also in humans disturbances in thyroid hormone system, weight of reproductive organs and concentrations of sex hormones associated with PBDEs serum concentrations were found. Exposure to PBDEs during pregnancy may lead to slower mental and psychomotor development in infants. In this paper the results of previous animal and human studies are reviewed.

Developmental thyroid hormone insufficiency and brain development: a role for brain-derived neurotrophic factor (BDNF)?

Thyroid hormones (TH) are essential for normal brain development. Even modest degrees of TH disruption experienced in utero can result in neuropsychological deficits in children despite normal thyroid status at birth. Neurotrophins have been implicated in a host of brain cellular functions, and in particular, brain-derived neurotrophic factor (BDNF) has a well documented role in development and function of the nervous system. A number of laboratories have reported the effects of TH administration or severe deprivation on neurotrophin expression in brain. This review provides an overview and update of recent developments in the thyroid field as they relate to the nervous system. Secondly, we describe an animal model of low level TH insufficiency that is more relevant for studying the neurological consequences associated with the modest TH perturbations of subclinical hypothyroidism, or that would be anticipated from exposure to environmental contaminants with a mode-of-action that involves the thyroid. Finally, we review the available in vivo literature on TH-mediated alterations in neurotrophins, particularly BDNF, and discuss their possible contribution to brain impairments associated with TH insufficiency. The observations of altered BDNF protein and gene expression have varied as a function of hypothyroid model, age, and brain region assessed. Only a handful of studies have investigated the relationship of neurotrophins and TH using models of TH deprivation that are not severe, and dose-response information is sparse. Differences in the models used, species, doses, regions assessed, age at assessment, and method employed make it difficult to reach a consensus. Based on the available literature, the case for a direct role for BDNF in thyroid-mediated effects in the brain is not compelling. We conclude that delineation of the potential role of neurotrophins in TH-mediated neuronal development may be more fruitful by examining additional neurotrophins (e.g., nerve growth factor), moderate degrees of TH insufficiency, and younger ages. We further suggest that investigation of BDNF invoked by synaptic activation (i.e., plasticity, enrichment, trauma) may serve to elucidate a role of thyroid hormone in BDNF-regulated synaptic function.

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.

Genome-wide analysis of Pax8 binding provides new insights into thyroid functions

Background

The transcription factor Pax8 is essential for the differentiation of thyroid cells. However, there are few data on genes transcriptionally regulated by Pax8 other than thyroid-related genes. To better understand the role of Pax8 in the biology of thyroid cells, we obtained transcriptional profiles of Pax8-silenced PCCl3 thyroid cells using whole genome expression arrays and integrated these signals with global cis-regulatory sequencing studies performed by ChIP-Seq analysis

Results

Exhaustive analysis of Pax8 immunoprecipitated peaks demonstrated preferential binding to intragenic regions and CpG-enriched islands, which suggests a role of Pax8 in transcriptional regulation of orphan CpG regions. In addition, ChIP-Seq allowed us to identify Pax8 partners, including proteins involved in tertiary DNA structure (CTCF) and chromatin remodeling (Sp1), and these direct transcriptional interactions were confirmed in vivo. Moreover, both factors modulate Pax8-dependent transcriptional activation of the sodium iodide symporter (Nis) gene promoter. We ultimately combined putative and novel Pax8 binding sites with actual target gene expression regulation to define Pax8-dependent genes. Functional classification suggests that Pax8-regulated genes may be directly involved in important processes of thyroid cell function such as cell proliferation and differentiation, apoptosis, cell polarity, motion and adhesion, and a plethora of DNA/protein-related processes.

Conclusion

Our study provides novel insights into the role of Pax8 in thyroid biology, exerted through transcriptional regulation of important genes involved in critical thyrocyte processes. In addition, we found new transcriptional partners of Pax8, which functionally cooperate with Pax8 in the regulation of thyroid gene transcription. Besides, our data demonstrate preferential location of Pax8 in non-promoter CpG regions. These data point to an orphan CpG island-mediated mechanism that represents a novel role of Pax8 in the transcriptional output of the thyrocyte.

Formation of excess sublobules in the cerebellum of hypothyroid rats

Cerebellar folia may increase in number in hypothyroid rats (Lauder et al., 1974; Hasebe et al., 2008a). In this study, we aimed to confirm the formation of an excess sublobule and to determine whether excess sublobules are consistently formed in conserved positions in hypothyroid rats. Instead of the foliation pattern partitioned by cerebellar fissures, we employed the bifurcation pattern of the internal granular layer for investigation of complexity of the cerebellar cortex in hypothyroid rats. The basic foliation pattern of the cerebellum was intact in hypothyroid rats, but lobules III to IX frequently showed an increase in the number of sublobules. The excess sublobules were mainly found in the folia and along the shallow region of the fissure. In other words, the excess sublobules were not located in random locations but rather in specific locations. The area in the internal granular layer of lobules V to IX was significantly larger than that in control rats. From the increased area of the internal granular layer it may be inferred that internal granular cells increase in number than those in normal rats. In our study, regions within the cerebellum that show an excess of sublobules correlate with regions that show an intermediate to late-forming internal granular layer (Altman, 1969). Our observations fit with the view that excess sublobules are formed by the external granular layer showing prolonged cell proliferation and hypothyroidism predominantly has an adverse impact on the intermediate to late phases in development of the internal granular layer.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.

Congenital hypothyroidism with neurological and respiratory alterations: a case detected using a variable diagnostic threshold for TSH

We report a case of congenital hypothyroidism (CH) with neurological and respiratory alterations due to a heterozygotic c.374-1G > A mutation of TITF1/NKX2-1. The hypothyroidism was detected using a neonatal screening protocol in which the thyroid stimulating hormone (TSH) threshold is re-set each day on the basis of within-day variability and between-day variation. In this case, the threshold on the day of the initial analysis was 8.2 mIU/L, and the measured TSH level in heel-prick blood was 8.3 mIU/L.

Levels and patterns of hydroxylated polychlorinated biphenyls (OH-PCBs) and their associations with thyroid hormones in hooded seal (Cystophora cristata) mother-pup pairs

Blood (plasma/serum) samples from 14 adult female and their pups (1-4 days old) captured in the West Ice, east of Greenland were analysed for concentrations of total and free thyroxine and triiodothyronine (TT4, FT4, TT3, FT3), and hydroxylated polychlorinated biphenyls (OH-PCBs). The levels of all thyroid hormones (THs) were significantly higher in pups than in mothers. Sum OH-PCB levels (ΣOH-PCBs: 4-OH-CB107, 3'-OH-CB138, 4-OH-CB146, 4'-OH-CB172, 4-OH-CB187) were significantly higher in mothers (3.98 ± 1.55 pmol/g; 1.40 ± 0.54 ng/g wet weight) as compared to pups (1.95 ± 0.78 pmol/g; 0.68 ± 0.28 ng/g wet weight). Plasma levels of TT4 and FT4 in mothers increased as a function of pup age, as did levels of individual OH-PCBs in both mothers and pups. The pattern of OH-PCBs in the pups was similar to their mothers. We suggest that OH-PCBs found in pups are transferred from their mothers during gestation and that the transfer also continues after parturition via milk. Principal component analysis (PCA) showed that in pups, 4-OH-CB107 and 3'-OH-CB138 were negatively associated with FT4:FT3 and TT3:FT3 ratios, respectively. These relationships were confirmed by partial correlation analysis correcting for pup age. PCA suggested that 4'-OH-CB172 and 4-OH-CB187 were negatively associated with TT3 in mothers. However, this was not confirmed by correlation tests. Although statistical relationships should be interpreted with caution, the study indicates that young developing seals are more sensitive compared to adults with respect to TH-related effects of OH-PCBs.

Thyroid hormone deficiency disrupts rat eye neurodevelopment

Clinical and experimental studies have highlighted the role played by thyroid hormones (TH) in neural and neuro-sensorial development. However, knowledge on TH mechanisms on the developing visual system is still incomplete. To uncover TH actions on the eyes and vision we carried out a microscopical study on the role of TH in the developing retina and optic nerve, in a rat model of controlled TH deficiency (THD). Morphometric and stereological analyses of the retina and optic nerve showed a reduction in the volume of the eye (p<0.001) and optic nerve cross-sectional area (p<0.001), and thinning of the retinal layers (p<0.001). Glial development and myelination was significantly delayed in the THD optic nerves (p<0.001), as compared to controls. The data indicate that TH play an essential role in neuro-retinogenesis. Substitutive TH therapy in critical periods, should be considered in hypothyroidism-related eye disorders as well as neurodegenerative retinal processes.

Levothyroxine replacement therapy and refractory hypotension out of transitional period in preterm infants

BACKGROUND

Recent studies suggest that refractory hypotension from causes other than septicaemia or cardiac failure is common in extremely preterm infants even out of the transitional period. Marked response to low-dose cortisol suggests underlying adrenal insufficiency, although the exact mechanism remains unknown.

METHODS

To investigate potential triggers for and related short-term outcomes of early-onset (<Day 7) and late-onset (≥Day 7) refractory hypotension, clinical data for 70 infants <30 weeks gestation were assessed.

RESULTS

The incidence of early-onset refractory hypotension (n=7) was correlated with younger gestational ages <26 weeks (P < 0.05), whereas the incidence of late-onset refractory hypotension (n=14) was correlated with younger gestational ages and levothyroxine supplementation (P<0.05 and 0.01, respectively). The incidence of both early- and late-onset refractory hypotension was correlated with risks of short-term adverse outcomes such as prolonged mechanical ventilation and hospital stay.

CONCLUSIONS

Levothyroxine supplementation was identified as an independent variable correlated with an increased incidence of refractory hypotension out of the transitional period; as seen in hypothyroidism with Addison's disease, the immature hypothalamic-pituitary-adrenal axis may not respond properly to the increased demand for cortisol, which may precipitate premature infants into refractory hypotension. Following the administration of levothyroxine, preterm infants may have to be carefully monitored for early signs of refractory hypotension.

Human testicular orphan receptor 4 enhances thyroid hormone receptor signaling

The thyroid hormone receptor (TR) and human testicular orphan receptor 4 (TR4) belong to the nuclear hormone receptor superfamily. They are ligand-dependent transcription factors. TR and TR4 bind to a similar thyroid response element (TRE), known as a direct repeat with four nucleotide spacing (DR4). This study examined the possible interaction or cross-talking between those two receptors. We hypothesized that protein-protein interaction between TR4 and TR may promote TR-mediated transcriptional activity. Glutathione S-transferase pull-down and immunoprecipitation assays showed direct interaction between TR and TR4. Electrophoretic mobility-shift assay demonstrated that TR and TR4 could co-occupy the same TRE. The interaction between TR4 and TR may enhance regulation of genes targeted by TR, such as furin, fibrinogen, cdk2 and p21 expression. We found that TR4 function is similar with TR as TR4 alone could regulate expression of some TR target genes, and could increase cell migration or inhibit cell proliferation. Importantly, the TR-dependent inhibition of cell proliferation and stimulation of cell migration are more enhanced in the HepG2-TR cells stably over-expressing TR4. Overall, TR4 not only has modulation abilities similar to TR but also can cross-talk with TR and promote the TR signaling pathway.

T3 differentially regulates TRH expression in developing hypothalamic neurons in vitro

Triiodothyronine (T3) plays an important role during development of the central nervous system. T3 effects on gene expression are determined in part by the type of thyroid hormone receptors (TRs) expressed in a given cell type. Previous studies have demonstrated that thyrotropin releasing hormone (TRH) transcription in the adult hypothalamus is subjected to negative regulation by thyroid hormones. However, the role of T3 on the development of TRH expression is unknown. In this study we used primary cultures derived from 17-day-old fetal rat hypothalamus to analyze the effects of T3 on TRH gene expression during development. T3 increased TRH mRNA expression in immature cultures, but decreased it in mature cultures. In addition, T3 up-regulated TRalpha1 and TRbeta2 mRNA expression. TRalpha1 expression coincided chronologically with that of TRH in the rat hypothalamus in vivo. Maturation of TRH expression in the hypothalamus may involve T3 acting through TRalpha1.

Abnormal growth of the corticospinal axons into the lumbar spinal cord of the hyt/hyt mouse with congenital hypothyroidism

Thyroid hormone deficiency may cause severe neurological disorders resulting from developmental deficits of the central nervous system. The mutant hyt/hyt mouse, characterized by fetal-onset, life-long hypothyroidism resulting from a point mutation of the thyroid-stimulating hormone receptor of the thyroid gland, displays a variety of abnormalities in motor behavior that are likely associated with dysfunctions of specific brain regions and a defective corticospinal tract (CST). To test the hypothesis that fetal and neonatal hypothyroidism cause abnormal CST development, the growth of the CST was investigated in hypothyroid hyt/hyt mice and their euthyroid progenitors, the BALB/cByJ mice. Anterograde labeling with biotinylated dextran amine demonstrated a decrease in the number of CST axons in the hyt/hyt mouse at the first lumbar level at postnatal day (P) 10. After retrograde tracing with fast blue (FB), fewer FB-labeled neurons were found in the motor cortex, the red nucleus, and the lateral vestibular nucleus of the hyt/hyt mouse. At the fourth lumbar level, the hyt/hyt mouse also showed smaller CST cross-sectional areas and significantly lower numbers of unmyelinated axons, myelinated axons, and growth cones within the CST during postnatal development. At P10, the hyt/hyt mouse demonstrated significantly lower immunoreactivity of embryonic neural cell adhesion molecule in the CST at the seventh cervical level, whereas the expression of growth-associated protein 43 remained unchanged. Our study demonstrated an abnormal development of the CST in the hyt/hyt mouse, manifested by reduced axon quantity and retarded growth pattern at the lumbar spinal cord.

Trials with thyroid hormone in preterm infants: clinical and neurodevelopmental effects

A large number of articles exist on thyroid hormone function and its clinical correlates, but only a few exist on trials with thyroid hormones in premature infants. Most of these trials had clinical short-term endpoints, while only one trial had a long-term neurodevelopmental endpoint. None of the trials reported changes in mortality and morbidities. A trend toward a lower occurrence of patent ductus arteriosus is found in thyroid hormone treated infants. A gestational age-dependent effect of thyroxine on neurodevelopmental outcome was found in post-hoc subgroup analyses up until the age of 10 years. Thyroxine treatment was associated with improved mental, motor, and neurological outcomes in infants <28 weeks gestation, but with worse mental and neurological outcome in infants of 29 weeks gestation. Future trials should focus on neurodevelopmental outcomes. Continuous administration of thyroid hormone may be more effective than bolus administration.

The solution structure of DNA-free Pax-8 paired box domain accounts for redox regulation of transcriptional activity in the pax protein family

Pax-8 is a transcription factor belonging to the PAX genes superfamily and its crucial role has been proven both in embryo and in the adult organism. Pax-8 activity is regulated via a redox-based mechanism centered on the glutathionylation of specific cysteines in the N-terminal region (Cys45 and Cys57). These residues belong to a highly evolutionary conserved DNA binding site: the Paired Box (Prd) domain. Crystallographic protein-DNA complexes of the homologues Pax-6 and Pax-5 showed a bipartite Prd domain consisting of two helix-turn-helix (HTH) motifs separated by an extended linker region. Here, by means of nuclear magnetic resonance, we show for the first time that the HTH motifs are largely defined in the unbound Pax-8 Prd domain. Our findings contrast with previous induced fit models, in which Pax-8 is supposed to largely fold upon DNA binding. Importantly, our data provide the structural basis for the enhanced chemical reactivity of residues Cys45 and Cys57 and explain clinical missense mutations that are not obviously related to the DNA binding interface of the paired box domain. Finally, sequence conservation suggests that our findings could be a general feature of the Pax family transcription factors.

Non-genomic actions of thyroid hormone in brain development

Thyroid hormone (TH) is essential for neuronal migration and synaptogenesis in the developing brain. Assembly of neuronal circuits depends on guidance cues provided by the extracellular matrix. These cues are interpreted by the migrating neuron and its growing neurites through transmembrane signaling proteins anchored in place by the actin cytoskeleton. One of the best examples of a non-genomic action of thyroid hormone is its dynamic regulation of the number and quantity of actin fibers in astrocytes. Thyroxine (T4) and its transcriptionally inactive metabolite, 3',5',3-triiodothyronine (reverse T3) are responsible for modulating microfilament organization, while the transcriptional activator, 3',3,5-triiodothyronine (T3) is inert. The biological consequence of the loss of the actin filaments in astrocytes is the inability of the cell to anchor laminin, to its cell surface, and the loss of this key guidance molecule interrupts neurite pathfinding and neuronal migration. These data provide the essentials to construct a physiological pathway where TH-dependent regulation of the polymerization state of actin in the astrocyte and the developing neuron modulates the production and recognition of guidance cues--cues that if disrupted lead to abnormal neuronal migration and neuronal process formation--and lead to the morphological deficits observed in the cretinous brain.

PAX3 expression in primary melanomas and nevi

Melanoma is responsible for an estimated 62,000 new American cancer diagnoses and is projected to cause nearly 8000 deaths in 2008 alone. Although the histogenesis of the tumor is not well understood, it is thought to originate from a rare melanocyte stem cell that resides in the skin. The transcription factor PAX3 has a well-established role in the development of melanocytes during embryogenesis, and has recently been characterized as a molecular switch in the mature melanocyte. Based on this function, PAX3 promotes a melanocytic phenotype but blocks terminal differentiation. This mechanism may also contribute to the uncontrolled cell growth and loss of terminal differentiation in melanomas. Here, we find PAX3 expression in 8/8 melanoma cell lines. We also find that PAX3 is commonly expressed in primary melanoma samples (21/58) but significantly less frequently in benign pigmented lesions (9/75). Further analysis of our melanoma set revealed that PAX3 expression is strongly correlated with younger patients with low or no evidence of sun damage. Our data suggest that PAX3-expressing melanomas may be less environmentally dependent and more genetically linked.

Thyroid hormones, learning and memory

Thyroid hormones (THs), T3 and T4, have many physiological actions and are essential for normal behavioral, intellectual and neurological development. THs have a broad spectrum of effects on the developing brain and mediate important effects within the CNS throughout life. Insufficient maternal iodine intake during gestation and TH deficiency during human development are associated to pathological alterations such as cretinism and mental retardation. In adulthood, thyroid dysfunction is related to neurological and behavioral abnormalities, including memory impairment. Analysis of different experimental models suggests that most of the effects on cognition as a result of thyroid dysfunction rely on hippocampal modifications. Insufficiency of THs during development thus alters hippocampal synaptic function and impairs behavioral performance of hippocampal-dependent learning and memory tasks that persist in euthyroid adult animals. In the present review, we summarize the current knowledge obtained by clinical observations and experimental models that shows the importance of THs in learning and mnemonic processes.

Autism: transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents

The incidence and prevalence of autism have increased during the past two decades. Despite comprehensive genetic studies the cause of autism remains unknown. This review emphasizes the potential importance of environmental factors in its causation. Alterations of cortical neuronal migration and cerebellar Purkinje cells have been observed in autism. Neuronal migration, via reelin regulation, requires triiodothyronine (T3) produced by deiodination of thyroxine (T4) by fetal brain deiodinases. Experimental animal models have shown that transient intrauterine deficits of thyroid hormones (as brief as 3 days) result in permanent alterations of cerebral cortical architecture reminiscent of those observed in brains of patients with autism. I postulate that early maternal hypothyroxinemia resulting in low T3 in the fetal brain during the period of neuronal cell migration (weeks 8-12 of pregnancy) may produce morphological brain changes leading to autism. Insufficient dietary iodine intake and a number of environmental antithyroid and goitrogenic agents can affect maternal thyroid function during pregnancy. The most common causes could include inhibition of deiodinases D2 or D3 from maternal ingestion of dietary flavonoids or from antithyroid environmental contaminants. Some plant isoflavonoids have profound effects on thyroid hormones and on the hypothalamus-pituitary axis. Genistein and daidzein from soy (Glycine max) inhibit thyroperoxidase that catalyzes iodination and thyroid hormone biosynthesis. Other plants with hypothyroid effects include pearl millet (Pennisetum glaucum) and fonio millet (Digitaria exilis); thiocyanate is found in Brassicae plants including cabbage, cauliflower, kale, rutabaga, and kohlrabi, as well as in tropical plants such as cassava, lima beans, linseed, bamboo shoots, and sweet potatoes. Tobacco smoke is also a source of thiocyanate. Environmental contaminants interfere with thyroid function including 60% of all herbicides, in particular 2,4-dichlorophenoxyacetic acid (2,4-D), acetochlor, aminotriazole, amitrole, bromoxynil, pendamethalin, mancozeb, and thioureas. Other antithyroid agents include polychlorinated biphenyls (PCBs), perchlorates, mercury, and coal derivatives such as resorcinol, phthalates, and anthracenes. A leading ecological study in Texas has correlated higher rates of autism in school districts affected by large environmental releases of mercury from industrial sources. Mercury is a well known antithyroid substance causing inhibition of deiodinases and thyroid peroxidase. The current surge of autism could be related to transient maternal hypothyroxinemia resulting from dietary and/or environmental exposure to antithyroid agents. Additional multidisciplinary epidemiological studies will be required to confirm this environmental hypothesis of autism.

Health status, psychological symptoms, mood, and cognition in L-thyroxine-treated hypothyroid subjects

OBJECTIVE

Many hypothyroid subjects receiving L-thyroxine (L-T4) complain of psychological symptoms or cognitive dysfunction. However, there is limited validated information on these self-reports.

DESIGN

Cross-sectional comparison of 20 euthyroid and 34 treated hypothyroid subjects, aged 20-45 years, with normal thyroid-stimulating hormone (TSH) levels. Subjects underwent the following validated measures: Short Form 36 (SF-36); Symptom Checklist 90-Revised (SCL-90-R); Profile of Mood States (POMS); and tests of declarative memory (Paragraph Recall, Complex Figure), working memory (N-Back, Subject Ordered Pointing, Digit Span Backwards), and motor learning (Pursuit Rotor).

MAIN OUTCOMES

L-T4-treated subjects had higher mean TSH and free T4 levels, but free triiodothyronine (T3) levels were comparable to controls. L-T4-treated subjects had decrements on SF-36 and SCL-90-R summary scales and subscales. These subjects performed slightly worse on N-Back and Pursuit Rotor tests. Neither TSH nor thyroid hormone levels were associated with performance on psychological or cognitive measures.

CONCLUSIONS

This group of L-T4-treated subjects had decrements in health status, psychological function, working memory, and motor learning compared to euthyroid controls. Higher mean TSH levels suggest this may be related to suboptimal treatment, although there were no correlations between TSH levels and outcomes. These findings are limited by potential selection bias, and randomized studies targeting different TSH levels and memory subdomains would clarify these issues.