The thyroid hormone nuclear receptors and the Wnt/β-catenin pathway: An intriguing liaison

Targeting Androgen, Thyroid Hormone, and Vitamin A and D Receptors to Treat Prostate Cancer

The nuclear hormone family of receptors regulates gene expression. The androgen receptor (AR), upon ligand binding and homodimerization, shuttles from the cytosol into the nucleus to activate gene expression. Thyroid hormone receptors (TRs), retinoic acid receptors (RARs), and the vitamin D receptor (VDR) are present in the nucleus bound to chromatin as a heterodimer with the retinoid X receptors (RXRs) and repress gene expression. Ligand binding leads to transcription activation. The hormonal ligands for these receptors play crucial roles to ensure the proper conduct of very many tissues and exert effects on prostate cancer (PCa) cells. Androgens support PCa proliferation and androgen deprivation alone or with chemotherapy is the standard therapy for PCa. RARγ activation and 3,5,3'-triiodo-L-thyronine (T3) stimulation of TRβ support the growth of PCa cells. Ligand stimulation of VDR drives growth arrest, differentiation, and apoptosis of PCa cells. Often these receptors are explored as separate avenues to find treatments for PCa and other cancers. However, there is accumulating evidence to support receptor interactions and crosstalk of regulatory events whereby a better understanding might lead to new combinatorial treatments.

Effect of thyroid disruption on ovarian development following maternal exposure to Bisphenol S

Thyroid hormones play a crucial role in numerous physiological processes, including reproduction. Bisphenol S (BPS) is a structural analog of Bisphenol A known for its toxic effects. Interference of this substitute with normal thyroid function has been described. To investigate the effect of thyroid disruption on ovarian development following maternal exposure to BPS, female rats were exposed, daily, to either AT 1-850 (a thyroid hormone receptor antagonist) (10 nmol/rat) or BPS (0.2 mg/kg) during gestation and lactation. The effects on reproductive outcome, offspring development, histological structures, hormone levels, oxidative status, cytoskeleton proteins expression, and oocyte development gene expression were examined. Our results are in favor of offspring ovarian development disruption due to thyroid disturbance in adult pregnant females. During both fetal and postnatal stages, BPS considerably altered the histological structure of the thyroid tissue as well as oocyte and follicular development, which led to premature ovarian failure and stimulation of oocyte atresia, being accompanied with oxidative stress, hypothalamic-pituitary-ovarian axis disorders, and cytoskeletal dynamic disturbance. Crucially, our study underscores that BPS may induce reproductive toxicity by blocking nuclear thyroid hormone receptors, evidenced by the parallelism and the perfect meshing between the data obtained following exposure to AT 1-850 and those after the treatment by this substitute.

Deiodinase inhibition impairs the formation of the three posterior swim bladder tissue layers during early embryonic development in zebrafish

Thyroid hormone system disruption (THSD) negatively affects multiple developmental processes and organs. In fish, inhibition of deiodinases, which are enzymes crucial for (in)activating thyroid hormones (THs), leads to impaired swim bladder inflation. Until now, the underlying mechanism has remained largely unknown. Therefore, the objective of this study was to identify the process during swim bladder development that is impacted by deiodinase inhibition. Zebrafish embryos were exposed to 6 mg/L iopanoic acid (IOP), a model deiodinase inhibitor, during 8 different exposure windows (0-60, 60-120, 24-48, 48-72, 72-96, 96-120, 72-120 and 0-120 h post fertilization (hpf)). Exposure windows were chosen based on the three stages of swim bladder development: budding (24-48 hpf), pre-inflation, i.e., the formation of the swim bladder tissue layers (48-72 hpf), and inflation phase (72-120 hpf). Exposures prior to 72 hpf, during either the budding or pre-inflation phase (or both), impaired swim bladder inflation, while exposure during the inflation phase did not. Based on our results, we hypothesize that DIO inhibition before 72 hpf leads to a local decrease in T3 levels in the developing swim bladder. Gene transcript analysis showed that these TH level alterations disturb both Wnt and hedgehog signaling, known to be essential for swim bladder formation, eventually resulting in impaired development of the swim bladder tissue layers. Improper development of the swim bladder impairs swim bladder inflation, leading to reduced swimming performance. This study demonstrates that deiodinase inhibition impacts processes underlying the formation of the swim bladder and not the inflation process, suggesting that these processes primarily rely on maternal rather than endogenously synthetized THs since TH measurements showed that THs were not endogenously synthetized during the sensitive period.

An atlas of genetic scores to predict multi-omic traits

The use of omic modalities to dissect the molecular underpinnings of common diseases and traits is becoming increasingly common. But multi-omic traits can be genetically predicted, which enables highly cost-effective and powerful analyses for studies that do not have multi-omics1. Here we examine a large cohort (the INTERVAL study2; n = 50,000 participants) with extensive multi-omic data for plasma proteomics (SomaScan, n = 3,175; Olink, n = 4,822), plasma metabolomics (Metabolon HD4, n = 8,153), serum metabolomics (Nightingale, n = 37,359) and whole-blood Illumina RNA sequencing (n = 4,136), and use machine learning to train genetic scores for 17,227 molecular traits, including 10,521 that reach Bonferroni-adjusted significance. We evaluate the performance of genetic scores through external validation across cohorts of individuals of European, Asian and African American ancestries. In addition, we show the utility of these multi-omic genetic scores by quantifying the genetic control of biological pathways and by generating a synthetic multi-omic dataset of the UK Biobank3 to identify disease associations using a phenome-wide scan. We highlight a series of biological insights with regard to genetic mechanisms in metabolism and canonical pathway associations with disease; for example, JAK-STAT signalling and coronary atherosclerosis. Finally, we develop a portal ( https://www.omicspred.org/ ) to facilitate public access to all genetic scores and validation results, as well as to serve as a platform for future extensions and enhancements of multi-omic genetic scores.

Hyperthyroidism and Wnt Signaling Pathway: Influence on Bone Remodeling

Graves' disease is an autoimmune disease of the thyroid gland, characterized by increased production of thyroid hormones, which can affect many different organ systems in the body. Among other problems, it can cause disorders of the skeletal system, shortening the bone remodeling cycle and causing a decrease in bone density. The Wnt cascade signaling pathway and the β-catenin, as a part of the canonical Wnt pathway, also play roles in maintaining bone mass. Inhibition of the Wnt pathway can cause bone loss, and its stimulation can increase it. The Wnt signaling pathway influences the effectiveness of thyroid hormones by affecting receptors for thyroid hormones and deiodinase, while thyroid hormones can change levels of β-catenin within the cell cytoplasm. This indicates that the Wnt pathway and thyroid hormone levels, including hyperthyroidism, are linked and may act together to change bone density. In this review article, we attempt to explain the interplay between thyroid hormones and the Wnt pathway on bone density, with a focus on directions for further research and treatment options.

Hippocampal dentate gyri proteomics reveals Wnt signaling involvement in the behavioral impairment in the THRSP-overexpressing ADHD mouse model

Children with attention-deficit/hyperactivity disorder (ADHD) often struggle with impaired executive function, temporal processing, and visuospatial memory, hallmarks of the predominantly inattentive presentation (ADHD-PI), subserved by the hippocampus. However, the specific genes/proteins involved and how they shape hippocampal structures to influence ADHD behavior remain poorly understood. As an exploratory tool, hippocampal dentate gyri tissues from thyroid hormone-responsive protein overexpressing (THRSP OE) mice with defining characteristics of ADHD-PI were utilized in proteomics. Integrated proteomics and network analysis revealed an altered protein network involved in Wnt signaling. Compared with THRSP knockout (KO) mice, THRSP OE mice showed impaired attention and memory, accompanied by dysregulated Wnt signaling affecting hippocampal dentate gyrus cell proliferation and expression of markers for neural stem cell (NSC) activity. Also, combined exposure to an enriched environment and treadmill exercise could improve behavioral deficits in THRSP OE mice and Wnt signaling and NSC activity. These findings show new markers specific to the ADHD-PI presentation, converging with the ancient and evolutionary Wnt signaling pathways crucial for cell fate determination, migration, polarity, and neural patterning during neurodevelopment. These findings from THRSP OE mice support the role of Wnt signaling in neurological disorders, particularly ADHD-PI presentation.

Kinesin family member 3A induces related diseases via wingless-related integration site/β-catenin signaling pathway

Kinesin family member 3A is an important motor protein that participates in various physiological and pathological processes, including normal tissue development, homeostasis maintenance, tumor infiltration, and migration. The wingless-related integration site/β-catenin signaling pathway is essential for critical molecular mechanisms such as embryonic development, organogenesis, tissue regeneration, and carcinogenesis. Recent studies have examined the molecular mechanisms of kinesin family member 3A, among which the wingless-related integration site/β-catenin signaling pathway has gained attention. The interaction between kinesin family member 3A and the wingless-related integration site/β-catenin signaling pathway is compact and complex but is fascinating and worthy of further study. The upregulation and downregulation of kinesin family member 3A influence many diseases and patient survival through the wingless-related integration site/β-catenin signaling pathway. Therefore, this review mainly focuses on describing the kinesin family member 3A and wingless-related integration site/β-catenin signaling pathways and their associated diseases.

Regulation of the THRA gene, encoding the thyroid hormone nuclear receptor TRα1, in intestinal lesions

The THRA gene, encoding the thyroid hormone nuclear receptor TRα1, is expressed in an increasing gradient at the bottom of intestinal crypts, overlapping with high Wnt and Notch activities. Importantly, THRA is upregulated in colorectal cancers, particularly in the high-Wnt molecular subtype. The basis of this specific and/or altered expression pattern has remained unknown. To define the mechanisms controlling THRA transcription and TRα1 expression, we used multiple in vitro and ex vivo approaches. Promoter analysis demonstrated that transcription factors important for crypt homeostasis and altered in colorectal cancers, such as transcription factor 7-like 2 (TCF7L2; Wnt pathway), recombining binding protein suppressor of hairless (RBPJ; Notch pathway), and homeobox protein CDX2 (epithelial cell identity), modulate THRA activity. Specifically, although TCF7L2 and CDX2 stimulated THRA, RBPJ induced its repression. In-depth analysis of the Wnt-dependent increase showed direct regulation of the THRA promoter in cells and of TRα1 expression in murine enteroids. Given our previous results on the control of the Wnt pathway by TRα1, our new results unveil a complex regulatory loop and synergy between these endocrine and epithelial-cell-intrinsic signals. Our work describes, for the first time, the regulation of the THRA gene in specific cell and tumor contexts.

Alterations of DNA methylation and expression of genes related to thyroid hormone metabolism in colon epithelium of obese patients

Background

Colorectal cancer is common among obese individuals. The purpose of the current study was to determine changes in DNA methylation status and mRNA expression of thyroid hormone receptor beta (THRB), as a tumor suppressor, and thyroid hormone inactivating enzyme, type 3 deiodinase (DIO3) genes, in human epithelial colon tissues of healthy obese individuals.

Methods

Colon biopsies were analyzed by methylation sensitive-high resolution melting (MS-HRM) to investigate promoter methylation of DIO3 and THRB, and by quantitative real-time polymerase chain reaction to assay expression of DIO3 and THRB mRNA on eighteen obese and twenty-one normal-weight healthy men.

Results

There was no significant difference in mean methylation levels at the THRB promoter region between the two groups. Nevertheless, obesity decreased THRB expression levels, significantly (P < 0.05; fold change: 0.19). Furthermore, obesity attenuated DNA methylation (P < 0.001) and enhanced mRNA expression of DIO3 (P < 0.05; fold change: 3).

Conclusions

Our findings suggest that obesity may alter expression of THRB and DIO3 genes through epigenetic mechanism. Alterations of THRB and DIO3 expressions may predispose colon epithelium of obese patients to neoplastic transformation.

Transcriptome Profiling of the Hippocampal Seizure Network Implicates a Role for Wnt Signaling during Epileptogenesis in a Mouse Model of Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (mTLE) is a life-threatening condition characterized by recurrent hippocampal seizures. mTLE can develop after exposure to risk factors such as febrile seizure, trauma, and infection. Within the latent period between exposure and onset of epilepsy, pathological remodeling events occur that contribute to epileptogenesis. The molecular mechanisms responsible are currently unclear. We used the mouse intrahippocampal kainite model of mTLE to investigate transcriptional dysregulation in the ipsilateral and contralateral dentate gyrus (DG), representing the epileptogenic zone (EZ) and peri-ictal zone (PIZ). DG were analyzed after 3, 7, and 14 days by RNA sequencing. In both the EZ and PIZ, transcriptional dysregulation was dynamic over the epileptogenic period with early expression of genes representing cell signaling, migration, and proliferation. Canonical Wnt signaling was upregulated in the EZ and PIZ at 3 days. Expression of inflammatory genes differed between the EZ and PIZ, with early expression after 3 days in the PIZ and delayed expression after 7-14 days in the EZ. This suggests that critical gene changes occur early in the hippocampal seizure network and that Wnt signaling may play a role within the latent epileptogenic period. These findings may help to identify novel therapeutic targets that could prevent epileptogenesis.

Thyroid hormone signaling in the intestinal stem cells and their niche

Several studies emphasized the function of the thyroid hormones in stem cell biology. These hormones act through the nuclear hormone receptor TRs, which are T3-modulated transcription factors. Pioneer work on T3-dependent amphibian metamorphosis showed that the crosstalk between the epithelium and the underlying mesenchyme is absolutely required for intestinal maturation and stem cell emergence. With the recent advances of powerful animal models and 3D-organoid cultures, similar findings have now begun to be described in mammals, where the action of T3 and TRα1 control physiological and cancer-related stem cell biology. In this review, we have summarized recent findings on the multiple functions of T3 and TRα1 in intestinal epithelium stem cells, cancer stem cells and their niche. In particular, we have highlighted the regulation of metabolic functions directly linked to normal and/or cancer stem cell biology. These findings help explain other possible mechanisms by which TRα1 controls stem cell biology, beyond the more classical Wnt and Notch signaling pathways.

ToxCast chemical library Wnt screen identifies diethanolamine as an activator of neural progenitor proliferation

Numerous autism spectrum disorder (ASD) risk genes are associated with Wnt signaling, suggesting that brain development may be especially sensitive to genetic perturbation of this pathway. Additionally, valproic acid, which modulates Wnt signaling, increases risk for ASD when taken during pregnancy. We previously found that an autism-linked gain-of-function UBE3A T485A mutant construct hyperactivated canonical Wnt signaling, providing a genetic means to elevate Wnt signaling above baseline levels. To identify environmental use chemicals that enhance or suppress Wnt signaling, we screened the ToxCast Phase I and II libraries in cells expressing this autism-linked UBE3A T485A gain-of-function mutant construct. Using structural comparisons, we identify classes of chemicals that stimulated Wnt signaling, including ethanolamines, as well as chemicals that inhibited Wnt signaling, such as agricultural pesticides, and synthetic hormone analogs. To prioritize chemicals for follow-up, we leveraged predicted human exposure data, and identified diethanolamine (DEA) as a chemical that stimulates Wnt signaling in UBE3A T485A -transfected cells, and has a high potential for prenatal exposure in humans. DEA enhanced proliferation in primary human neural progenitor cell lines (phNPC), but did not affect expression of canonical Wnt target genes in NPCs or primary mouse neuron cultures. Instead, we found DEA increased expression of the H3K9 methylation sensitive gene CALB1, consistent with competitive inhibition of the methyl donor enzymatic pathways.

Thyroid receptor β might be responsible for breast cancer associated with Hashimoto's thyroiditis: a new insight into pathogenesis

Breast cancer is the most common cancer affecting females worldwide. Often it is observed that women suffering from Hashimoto's thyroiditis exhibit a greater propensity towards development of breast cancer. The exact mechanism for the same is unknown. However, multiple experimental evidences suggest a significant role of thyroid receptor β (TR-β) in regulating cell growth and proliferation and thus play a potent role as a tumor suppressor in several cancers, including breast cancer. Thyroid receptor β shows anti-proliferative action through mediators like β-catenin, RUNX2, PI3K/AKT, and cyclin regulation. The present review explores the link between these pathways and how they may be dysregulated due to Hashimoto's thyroiditis. Further, we propose a new mechanism for cancer prognosis associated with Hashimoto's thyroiditis, which may lead to the development of TR-β targeting as a novel therapeutic approach.

Canonical Thyroid Hormone Receptor β Action Stimulates Hepatocyte Proliferation in Male Mice

CONTEXT

3,5,3'-L-triiodothyronine (T3) is a potent inducer of hepatocyte proliferation via the Wnt/β-catenin signaling pathway. Previous studies suggested the involvement of rapid noncanonical thyroid hormone receptor (TR) β signaling, directly activating hepatic Wnt/β-catenin signaling independent from TRβ DNA binding. However, the mechanism by which T3 increases Wnt/β-catenin signaling in hepatocytes has not yet been determined.

OBJECTIVE

We aimed to determine whether DNA binding of TRβ is required for stimulation of hepatocyte proliferation by T3.

METHODS

Wild-type (WT) mice, TRβ knockout mice (TRβ KO), and TRβ mutant mice with either specifically abrogated DNA binding (TRβ GS) or abrogated direct phosphatidylinositol 3 kinase activation (TRβ 147F) were treated with T3 for 6 hours or 7 days. Hepatocyte proliferation was assessed by Kiel-67 (Ki67) staining and apoptosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Activation of β-catenin signaling was measured in primary murine hepatocytes. Gene expression was analyzed by microarray, gene set enrichment analysis (GSEA), and quantitative reverse transcription polymerase chain reaction.

RESULTS

T3 induced hepatocyte proliferation with an increased number of Ki67-positive cells in WT and TRβ 147F mice (9.2% ± 6.5% and 10.1% ± 2.9%, respectively) compared to TRβ KO and TRβ GS mice (1.2% ± 1.1% and 1.5% ± 0.9%, respectively). Microarray analysis and GSEA showed that genes of the Wnt/β-catenin pathway-among them, Fzd8 (frizzled receptor 8) and Ctnnb1 (β-catenin)-were positively enriched only in T3-treated WT and TRβ 147F mice while B-cell translocation gene anti-proliferation factor 2 was repressed. Consequently, expression of Ccnd1 (CyclinD1) was induced.

CONCLUSIONS

Instead of directly activating Wnt signaling, T3 and TRβ induce key genes of the Wnt/β-catenin pathway, ultimately stimulating hepatocyte proliferation via CyclinD1. Thus, canonical transcriptional TRβ action is necessary for T3-mediated stimulation of hepatocyte proliferation.

Developmental thyroid disruption permanently affects the neuroglial output in the murine subventricular zone

Neural stem cells (NSCs) in the adult brain are a source of neural cells for brain injury repair. We investigated whether their capacity to generate new neurons and glia is determined by thyroid hormone (TH) during development because serum levels peak during postnatal reorganization of the main NSC niche, the subventricular zone (SVZ). Re-analysis of mouse transcriptome data revealed increased expression of TH transporters and deiodinases in postnatal SVZ NSCs, promoting local TH action, concomitant with a burst in neurogenesis. Inducing developmental hypothyroidism reduced NSC proliferation, disrupted expression of genes implicated in NSC determination and TH signaling, and altered the neuron/glia output in newborns. Three-month-old adult mice recovering from developmental hypothyroidism had fewer olfactory interneurons and underperformed on short-memory odor tests, dependent on SVZ neurogenesis. Our data provide readouts permitting comparison with adverse long-term events following thyroid disruptor exposure and ideas regarding the etiology of prevalent neurodegenerative diseases in industrialized countries.

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Thyroid hormone peak associates with a neurogenic wave in the postnatal murine SVZ

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Single-cell RNA-seq data show increased TH action in SVZ progenitors at that stage

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Developmental hypothyroidism disrupts neuroglial commitment and associated genes

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Transient developmental TH depletion impairs adult neurogliogenesis and olfaction

Effect assessment of reclaimed waters and carbamazepine exposure on the thyroid axis of Xenopus laevis: Gene expression modifications

Reclaimed water (RW) obtained from wastewater treatment plants (WWTP) is used for irrigation, groundwater recharge, among other potential uses. Although most pollutants are removed, traces of them are frequently found, which can affect organisms and alter the environment. The presence of a myriad of contaminants in RW makes it a complex mixture with very diverse effects and interactions. A previous study, in which tadpoles were exposed to RW and RW spiked with Carbamazepine (CBZ), presented slight thyroid gland stimulation, as suggested by the development acceleration of tadpoles and histological findings in the gland provoked by RW, regardless of the CBZ concentration. To complement this study, the present work analysed the putative molecular working mechanism by selecting six genes coding for the thyroid-stimulating hormone (TSHβ), thyroid hormone metabolising enzymes (DIO2, DIO3), thyroid receptors (THRA, THRB), and a thyroid hormone-induced DNA binding protein (Kfl9). Transcriptional activity was studied by Real-Time PCR (RT-PCR) in brains, hind limbs, and tails on exposure days 1, 7, and 21. No significant differences were observed between treatments for each time point, but slight alterations were noted when the time response was analysed. The obtained results indicate that the effects of RW or RW spiked with CBZ are negligible for the genes analysed during the selected exposure periods.

Thyroid Hormone Nuclear Receptor TRα1 and Canonical WNT Pathway Cross-Regulation in Normal Intestine and Cancer

A pivotal role of thyroid hormones and their nuclear receptors in intestinal development and homeostasis have been described, whereas their involvement in intestinal carcinogenesis is still controversial. In this perspective article we briefly summarize the recent advances in this field and present new data regarding their functional interaction with one of the most important signaling pathway, such as WNT, regulating intestinal development and carcinogenesis. These complex interactions unveil new concepts and will surely be of importance for translational research.

Colorectal cancer causes alteration of thyroid hormone profile in newly diagnosed patients

OBJECTIVES

Subcellular alteration of thyroid hormones (THs) signaling is proposed in many types of cancers. Some studies show deiodinase type 3, as an oncofetal protein, re-expresses in some cancer types. Therefore, we aimed to investigate the product of this enzyme, reverse triiodothyronine (rT3) in serum of newly diagnosed colorectal cancer (CRC) patients.

METHODS

In this cross-sectional study, blood from 38 laboratory-confirmed cases was taken, and serum levels of rT3, total T3 (triiodothyronine), total T4 (thyroxine), free T3, free T4, and thyroid-stimulating hormone (TSH) were detected by using an enzyme-linked immunosorbent assay.

RESULTS

The results illustrated that rT3 and free T3 levels increased in patients with early stages of colorectal cancer, despite normal levels of total T3, total T4, free T4, and TSH.

CONCLUSION

The elevation of rT3 in CRC patients can probably be due to the re-expression of deiodinase type 3 in CRC. Further research is needed to study the role of intracellular THs modulation in CRC and its impact on CRC treatment.

Chlorogenic Acid Ameliorates Damage Induced by Fluorene-9-Bisphenol in Porcine Sertoli Cells

4,4′-(9-Fluorenylidene) diphenol (BPFL, also known as BHPF and fluorene-9-bisphenol) is a novel bisphenol A substitute that is used in the plastics industry as an organic synthesis intermediate and is a potential endocrine disruptor. However, the deleterious effects of BPFL on porcine Sertoli cells (SCs) and the possible underlying mechanisms are still unclear. Chlorogenic acid (CA) is a free radical scavenger in the cellular antioxidant system that prevents oxidative damage and apoptosis. In the present research, we found that BPFL induced impairments in porcine SCs in a dose-dependent manner and that CA protected porcine SCs against BPFL exposure-induced impairments. Cell viability, proliferation and apoptosis assay results revealed that BPFL exposure could inhibit porcine SC proliferation and induce apoptosis, while CA supplementation ameliorated the effects of BPFL. Further analysis revealed that BPFL exposure induced oxidative stress, mitochondrial membrane potential dysfunction and DNA damage accumulation. Transcriptome analysis and further real-time quantitative PCR and Western blot results showed that BPFL exposure induced endoplasmic reticulum stress and apoptosis. Supplementation with CA dramatically ameliorated these phenotypes in BPFL-exposed porcine SCs. Overall, the present research reveals the possible underlying mechanisms by which BPFL exposure induced impairments and CA supplementation protected against these impairments in porcine SCs.

Thyroid hormone regulates abrupt skin morphogenesis during zebrafish postembryonic development

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

Murine intestinal stem cells are highly sensitive to modulation of the T3/TRα1-dependent pathway

The thyroid hormone T3 and its nuclear receptor TRα1 control gut development and homeostasis through the modulation of intestinal crypt cell proliferation. Despite increasing data, in-depth analysis on their specific action on intestinal stem cells is lacking. By using ex vivo 3D organoid cultures and molecular approaches, we observed early responses to T3 involving the T3-metabolizing enzyme Dio1 and the transporter Mct10, accompanied by a complex response of stem cell- and progenitor-enriched genes. Interestingly, specific TRα1 loss-of-function (inducible or constitutive) was responsible for low ex vivo organoid development and impaired stem cell activity. T3 treatment of animals in vivo not only confirmed the positive action of this hormone on crypt cell proliferation but also demonstrated its key action in modulating the number of stem cells, the expression of their specific markers and the commitment of progenitors into lineage-specific differentiation. In conclusion, T3 treatment or TRα1 modulation has a rapid and strong effect on intestinal stem cells, broadening our perspectives in the study of T3/TRα1-dependent signaling in these cells.

Natural toxic impact and thyroid signalling interplay orchestrates riverine adaptive divergence of salmonid fish

Adaptive radiation in fishes has been actively investigated over the last decades. Along with numerous well-studied cases of lacustrine radiation, some examples of riverine sympatric divergence have been recently discovered. In contrast to the lakes, the riverine conditions do not provide evident stability in the ecological gradients. Consequently, external factors triggering the radiation, as well as developmental mechanisms underpinning it, remain unclear. Herein, we present the comprehensive study of external and internal drivers of the riverine adaptive divergence of the salmonid fish Salvelinus malma. In the Kamchatka River, north-east Asia, this species splits in the reproductively isolated morphs that drastically differ in ecology and morphology: the benthivorous Dolly Varden (DV) and the piscivorous stone charr (SC). To understand why and how these morphs originated, we performed a series of field and experimental work, including common-garden rearing, comparative ontogenetic, physiological and endocrinological analyses, hormonal 'engineering' of phenotypes and acute toxicological tests. We revealed that the type of spawning ground acts as the decisive factor driving the radiation of S. malma. In contrast to DV spawning in the leaf krummholz zone, SC reproduces in the zone of coniferous forest, which litter has a toxic impact on developing fishes. SC enhances resistance to the toxicants via metabolism acceleration provided by the elevated thyroid hormone expenditure. These physiological changes lead to the multiple heterochronies resulting in a specific morphology and ecology of SC. Salvelinus malma represents a notable example of how the thyroid axis contributes to the generation of diverse phenotypic outcomes underlying the riverine sympatric divergence. Our findings, along with the paleoecology data concerning spruce forest distribution during the Pleistocene, provide an opportunity to reconstruct a scenario of S. malma divergence. Taken together, obtained results with the data of the role of thyroid hormones in the ontogeny and diversification of fishes contribute a resource to consider the thyroid axis as a prime director orchestrating the phenotypic plasticity promoting evolutionary diversification under the changing environmental conditions.

Identification of a novel subgroup of endometrial cancer patients with loss of thyroid hormone receptor beta expression and improved survival

BACKGROUND

Endometrial cancer (EC) is the most common gynecologic cancer in women, and the incidence of EC has increased by about 1% per year in the U. S over the last 10 years. Although 5-year survival rates for early-stage EC are around 80%, certain subtypes of EC that lose nuclear hormone receptor (NHR) expression are associated with poor survival rates. For example, estrogen receptor (ER)-negative EC typically harbors a worse prognosis compared to ER-positive EC. The molecular basis for the loss of NHR expression in endometrial tumors and its contribution to poor survival is largely unknown. Furthermore, there are no tools to systematically identify tumors that lose NHR mRNA expression relative to normal tissue. The development of such an approach could identify sets of NHR-based biomarkers for classifying patients into subgroups with poor survival outcomes.

METHODS

Here, a new computational method, termed receptLoss, was developed for identifying NHR expression loss in endometrial cancer relative to adjacent normal tissue. When applied to gene expression data from The Cancer Genome Atlas (TCGA), receptLoss identified 6 NHRs that were highly expressed in normal tissue and exhibited expression loss in a subset of endometrial tumors.

RESULTS

Three of the six identified NHRs - estrogen, progesterone, and androgen receptors - that are known to lose expression in ECs were correctly identified by receptLoss. Additionally, a novel association was found between thyroid hormone receptor beta (THRB) expression loss, increased expression of miRNA-146a, and increased rates of 5-year survival in the EC TCGA patient cohort. THRB expression loss occurs independently of estrogen and progesterone expression loss, suggesting the discovery of a distinct, clinically-relevant molecular subgroup.

CONCLUSION

ReceptLoss is a novel, open-source software tool to systematically identify NHR expression loss in cancer. The application of receptLoss to endometrial cancer gene expression data identified THRB, a previously undescribed biomarker of survival in endometrial cancer. Applying receptLoss to expression data from additional cancer types could lead to the development of biomarkers of disease progression for patients with any other tumor type. ReceptLoss can be applied to expression data from additional cancer types with the goal of identifying biomarkers of differential survival.

Thyroid Hormone Actions and Bone Remodeling – The Role of the Wnt Signaling Pathway

Thyroid hormones are indispensable for bone development and growth. Also in adults, bone mass maintenance is under the control of thyroid hormones. Preclinical and clinical studies established untreated hyperthyroidism as a cause for secondary osteoporosis with increased fracture risk. Thus, normal thyroid function is essential for bone health. Mechanistically, thyroid hormone excess accelerates bone turnover with predominant bone resorption. How thyroid hormones affect osteoblast and osteoclast functions, however, still remains ill-defined. The Wnt signaling pathway is a major determinant of bone mass and strength as it promotes osteoblastogenesis and bone formation, while inhibiting bone resorption. So far, only few studies investigated a possible link between thyroid hormones, bone metabolism and the Wnt pathway. In this review, we summarize the literature linking thyroid hormones to bone homeostasis through Wnt signaling and discuss its potential as a therapeutic approach to treat hyperthyroidism-induced bone loss.

Thyroid hormone regulation of neural stem cell fate: From development to ageing

In the vertebrate brain, neural stem cells (NSCs) generate both neuronal and glial cells throughout life. However, their neuro‐ and gliogenic capacity changes as a function of the developmental context. Despite the growing body of evidence on the variety of intrinsic and extrinsic factors regulating NSC physiology, their precise cellular and molecular actions are not fully determined. Our review focuses on thyroid hormone (TH), a vital component for both development and adult brain function that regulates NSC biology at all stages. First, we review comparative data to analyse how TH modulates neuro‐ and gliogenesis during vertebrate brain development. Second, as the mammalian brain is the most studied, we highlight the molecular mechanisms underlying TH action in this context. Lastly, we explore how the interplay between TH signalling and cell metabolism governs both neurodevelopmental and adult neurogenesis. We conclude that, together, TH and cellular metabolism regulate optimal brain formation, maturation and function from early foetal life to adult in vertebrate species.

Thyroid hormone (T3) is involved in inhibiting the proliferation of newborn calf Sertoli cells via the PI3K/Akt signaling pathway in vitro

The experiment was designed to study the effects of Thyroid hormone (T₃) on the proliferation and differentiation of newborn calf Sertoli cells (SCs) to provide a theoretical and practical basis for increased testicular semen production. In this experiment, the cck8 method was used to detect the effects of different concentrations of T₃ on the proliferation rate of newborn calf SCs. qPCR and Western Blot methods were used to explore the effects of T3 on the proliferation and differentiation of calves SCs and whether T₃ through Wnt/β-catenin and PI3K/Akt pathways can regulate the proliferation and differentiation of SCs. We found that dosage (T₃) and time correlated with proliferation inhibition of SC. T₃ inhibited the proliferation of SC by down-regulating cyclinD1, upregulating p21Cip, p27Kip1, and other cell-cycle factors. By up-regulating AR and down-regulating KRT-18, T3 promoted the maturated differentiation of SC. T₃ could not affect the expression of β-catenin in SC of newborn calf, indicating that T₃ may not regulate SCs proliferation through the Wnt pathway. T3 also negatively regulated the gene expression and protein levels of some genes in the PI3K/Akt signaling pathway. We concluded that T₃ inhibited newborn calf SCs proliferation through the PI3K/Akt signaling pathway and possibly promoted their differentiation.

Increased expression of the thyroid hormone nuclear receptor TRα1 characterizes intestinal tumors with high Wnt activity

Our previous work demonstrated a key function of the thyroid hormone nuclear receptor TRα1, a T3-modulated transcription factor, in controlling intestinal development and homeostasis via the Wnt and Notch pathways. Importantly, increased expression of TRα1 in the intestinal epithelium in a mutated Apc genetic background (vil-TRα1/Apc^+/1638N mice) accelerated tumorigenesis and contributed to a more aggressive tumor phenotype compared to that of the Apc mutants alone. Therefore, the aim of this study was to determine the relevance of this synergistic effect in human colorectal cancers and to gain insights into the mechanisms involved. We analyzed cohorts of patients by in silico and experimental approaches and observed increased TRα1 expression and a significant correlation between TRα1 levels and Wnt activity. TRα1 loss-of-function and gain-of-function in Caco2 cell lines not only confirmed that TRα1 levels control Wnt activity but also demonstrated the role of TRα1 in regulating cell proliferation and migration. Finally, upon investigation of the molecular mechanisms responsible for the Wnt-TRα1 association, we described the repression by TRα1 of several Wnt inhibitors, including Frzb, Sox17 and Wif1. In conclusion, our results underline an important functional interplay between the thyroid hormone nuclear receptor TRα1 and the canonical Wnt pathway in intestinal cancer initiation and progression. More importantly, we show for the first time that the expression of TRα1 is induced in human colorectal cancers.

Thyroid hormone receptor α1 as a novel therapeutic target for tissue repair

Analogies between the damaged tissue and developing organ indicate that a regulatory network that drives embryonic organ development may control aspects of tissue repair. In this regard, there is a growing body of experimental and clinical evidence showing that TH may be critical for recovery after injury. Especially TRα1 has been reported to play an essential role in cell proliferation and differentiation and thus in the process of repair/regeneration in the heart and other tissues. Patients after myocardial infarction, stroke or therapeutic interventions [such as PCI for coronary artery disease (CAD)] with lower TH levels appear to have increased morbidity and mortality. Accordingly, TH treatment in clinical settings of ischemia/reperfusion such as by-pass surgery seems to be cardioprotective against ischemic injury. Furthermore, TH therapy of donors is shown to result in organ preservation and increased numbers of donors and improved post-transplantation graft survival. TH and thyroid analogs may prove novel therapeutic agents for tissue repair.

Thyroid hormone receptor localization in target tissues

The thyroid hormone receptors, TRα1, TRβ1 and other subtypes, are members of the nuclear receptor superfamily that mediate the action of thyroid hormone signaling in numerous tissues to regulate important physiological and developmental processes. Their most well-characterized role is as ligand-dependent transcription factors; TRs bind thyroid hormone response elements in the presence or absence of thyroid hormone to facilitate the expression of target genes. Although primarily residing in the nucleus, TRα1 and TRβ1 shuttle rapidly between the nucleus and cytoplasm. We have identified multiple nuclear localization signals and nuclear export signals within TRα1 and TRβ1 that interact with importins and exportins, respectively, to mediate translocation across the nuclear envelope. More recently, enigmatic cytoplasmic functions have been ascribed to other TR subtypes, expanding the diversity of the cellular response to thyroid hormone. By integrating data on localization signal motifs, this review provides an overview of the complex interplay between TR's dynamic transport pathways and thyroid hormone signaling activities. We examine the variation in TR subtype response to thyroid hormone signaling, and what is currently known about regulation of the variety of tissue-specific localization patterns, including targeting to the nucleus, the mitochondria and the inner surface of the plasma membrane.

Thyroid hormone regulation of intestinal epithelial stem cell biology

The gastrointestinal tract is a well-characterized target of thyroid hormones and thyroid hormone nuclear receptors TRs, as extensively described in the literature. The paradigm is its important remodelling in amphibians during thyroid hormone-dependent metamorphosis. Interestingly, several studies have described the conservation of this hormonal signal during intestinal development in mammals. Additional data suggested that it may also play a role in intestinal homeostasis, stem cell physiology and progenitor commitment as well as in tumour development. It is worth underlining that in the mammalian intestine the functionality of the TRα1 receptor is coordinated and integrated with other signalling pathways, such as Wnt and Notch, specifically at the level of stem/progenitor cell populations. Here, we summarize these data and concepts and discuss this new role for thyroid hormones and the TRα1 receptor in the biology of intestinal epithelial precursor cells.

How thyroid hormone regulates transformation of larval epithelial cells into adult stem cells in the amphibian intestine

In the amphibian intestine during metamorphosis, a small number of larval epithelial cells dedifferentiate into adult stem cells that newly form the adult epithelium analogous to the mammalian counterpart, while most of them undergo apoptosis. Because this larval-to-adult intestinal remodeling can be experimentally induced by thyroid hormone (TH) both in vivo and in vitro, TH response genes identified in the Xenopus intestine provide us valuable clues to investigating how adult stem cells and their niche are formed during postembryonic development. Their expression and functional analyses by using the culture and recent transgenic (Tg) techniques have shed light on key signaling pathways essential for intestinal stem cell development. The present review focuses on such recent findings and discusses the evolutionally conserved roles of TH in development or maintenance of the stem cells which are common to the terrestrial vertebrate intestines.

Transcriptomics reveal an integrative role for maternal thyroid hormones during zebrafish embryogenesis

Thyroid hormones (THs) are essential for embryonic brain development but the genetic mechanisms involved in the action of maternal THs (MTHs) are still largely unknown. As the basis for understanding the underlying genetic mechanisms of MTHs regulation we used an established zebrafish monocarboxylic acid transporter 8 (MCT8) knock-down model and characterised the transcriptome in 25hpf zebrafish embryos. Subsequent mapping of differentially expressed genes using Reactome pathway analysis together with in situ expression analysis and immunohistochemistry revealed the genetic networks and cells under MTHs regulation during zebrafish embryogenesis. We found 4,343 differentially expressed genes and the Reactome pathway analysis revealed that TH is involved in 1681 of these pathways. MTHs regulated the expression of core developmental pathways, such as NOTCH and WNT in a cell specific context. The cellular distribution of neural MTH-target genes demonstrated their cell specific action on neural stem cells and differentiated neuron classes. Taken together our data show that MTHs have a role in zebrafish neurogenesis and suggest they may be involved in cross talk between key pathways in neural development. Given that the observed MCT8 zebrafish knockdown phenotype resembles the symptoms in human patients with Allan-Herndon-Dudley syndrome our data open a window into understanding the genetics of this human congenital condition.