Role of thyroid hormone in hepatic gene regulation, chromatin remodeling, and autophagy

Nuclear receptor corepressor 1 levels differentially impact the intracellular dynamics of mutant thyroid hormone receptors associated with resistance to thyroid hormone syndrome

Thyroid hormone receptor α1 (TRα1) undergoes nucleocytoplasmic shuttling and mediates gene expression in response to thyroid hormone (T3). In Resistance to Thyroid Hormone Syndrome α (RTHα), certain TRα1 mutants have higher affinity for nuclear corepressor 1 (NCoR1) and may form stable complexes that are not released in the presence of T3. Here, we examined whether NCoR1 modulates intranuclear mobility and nuclear retention of TRα1 or RTHα-associated mutants in transfected human cells, as a way of analyzing critical structural components of TRα1 and to further explore the correlation between mutations in TRα1 and aberrant intracellular trafficking. We found no significant difference in intranuclear mobility, as measured by fluorescence recovery after photobleaching, between TRα1 and select RTHα mutants, irrespective of NCoR1 expression. Nuclear-to-cytoplasmic fluorescence ratios of RTHα mutants, however, varied from TRα1 when NCoR1 was overexpressed, with a significant increase in nuclear retention for A263V and a significant decrease for A263S and R384H. In NCoR1-knockout cells, nuclear retention of A263S, A263V, P389R, A382P, C392X, and F397fs406X was significantly decreased compared to control (wild-type) cells. Luciferase reporter gene transcription mediated by TRα1 was significantly repressed by both NCoR1 overexpression and NCoR1 knockout. Most RTHα mutants showed minimal induction regardless of NCoR1 levels, but T3-mediated transcriptional activity was decreased for R384C and F397fs406X when NCoR1 was overexpressed, and also decreased for N359Y in NCoR1-knockout cells. Our results suggest a complex interaction between NCoR1 and RTHα mutants characterized by aberrant intracellular localization patterns and transcriptional activity that potentially arise from variable repressor complex stability, and may provide insight into RTHα pathogenesis on a molecular and cellular level.

APOE2 protects against Aβ pathology by improving neuronal mitochondrial function through ERRα signaling

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease and apolipoprotein E (APOE) genotypes (APOE2, APOE3, and APOE4) show different AD susceptibility. Previous studies indicated that individuals carrying the APOE2 allele reduce the risk of developing AD, which may be attributed to the potential neuroprotective role of APOE2. However, the mechanisms underlying the protective effects of APOE2 is still unclear.

METHODS

We analyzed single-nucleus RNA sequencing and bulk RNA sequencing data of APOE2 and APOE3 carriers from the Religious Orders Study and Memory and Aging Project (ROSMAP) cohort. We validated the findings in SH-SY5Y cells and AD model mice by evaluating mitochondrial functions and cognitive behaviors respectively.

RESULTS

The pathway analysis of six major cell types revealed a strong association between APOE2 and cellular stress and energy metabolism, particularly in excitatory and inhibitory neurons, which was found to be more pronounced in the presence of beta-amyloid (Aβ). Moreover, APOE2 overexpression alleviates Aβ1-42-induced mitochondrial dysfunction and reduces the generation of reactive oxygen species in SH-SY5Y cells. These protective effects may be due to ApoE2 interacting with estrogen-related receptor alpha (ERRα). ERRα overexpression by plasmids or activation by agonist was also found to show similar mitochondrial protective effects in Aβ1-42-stimulated SH-SY5Y cells. Additionally, ERRα agonist treatment improve the cognitive performance of Aβ injected mice in both Y maze and novel object recognition tests. ERRα agonist treatment increased PSD95 expression in the cortex of agonist-treated-AD mice.

CONCLUSIONS

APOE2 appears to enhance neural mitochondrial function via the activation of ERRα signaling, which may be the protective effect of APOE2 to treat AD.

The Impact of Anorexia Nervosa and the Basis for Non-Pharmacological Interventions

Anorexia nervosa is a psychiatric disorder with an unknown etiology that is characterized by an individual's preoccupation with their weight and body structure while denying the severity of their low body weight. Due to the fact that anorexia nervosa is multifaceted and may indicate the coexistence of genetic, social, hormonal, and psychiatric disorders, a description of non-pharmacological interventions can be used to ameliorate or reduce the symptoms of this condition. Consequently, the purpose of the present narrative review is to describe the profile's context in the anorexic person as well as the support they would require from their family and environment. In addition, it is aimed at examining preventative and non-pharmacological interventions, such as nutritional interventions, physical activity interventions, psychological interventions, psychosocial interventions, and physical therapy interventions. To reach the narrative review aims, a critical review was conducted utilizing both primary sources, such as scientific publications, and secondary sources, such as bibliographic indexes, web pages, and databases. Nutritional interventions include nutritional education and an individualized treatment for each patient, physical activity interventions include allowing patients to perform controlled physical activity, psychological interventions include family therapy and evaluation of the existence of other psychological disorders, psychosocial interventions include management of the relationship between the patient and social media and physical therapy interventions include relaxation massages and exercises to relieve pain. All these non-pharmacological interventions need to be individualized based on each patient's needs.

Thyroid hormone upregulates LAMP2 expression and lysosome activity

Thyroid hormone (T₃)-induced autophagy and its biological significance have been extensively investigated in recent years. However, limited studies to date have focused on the important role of lysosomes in autophagy. In this study, we explored the effects of T₃ on lysosomal protein expression and trafficking in detail. Our findings showed that T₃ activates rapid lysosomal turnover and expression of numerous lysosomal genes, including TFEB, LAMP2, ARSB, GBA, PSAP, ATP6V0B, ATP6V0D1, ATP6V1E1, CTSB, CTSH, CTSL, and CTSS, in a thyroid hormone receptor-dependent manner. In a murine model, LAMP2 protein was specifically induced in mice with hyperthyroidism. T₃-promoted microtubule assembly was significantly disrupted by vinblastine, resulting in accumulation of the lipid droplet marker PLIN2. In the presence of the lysosomal autophagy inhibitors bafilomycin A1, chloroquine and ammonium chloride, we observed substantial accumulation of LAMP2 but not LAMP1 protein. T₃ further enhanced the protein levels of ectopically expressed LAMP1 and LAMP2. Upon knockdown of LAMP2, cavities of lysosomes and lipid droplets accumulated in the presence of T₃, although the changes in LAMP1 and PLIN2 expression were less pronounced. More specifically, the protective effect of T₃ against ER stress-induced death was abolished by knockdown of LAMP2. Our collective results indicate that T₃ not only promotes lysosomal gene expression but also LAMP protein stability and microtubule assembly, leading to enhancement of lysosomal activity in digesting any additional autophagosomal burden.

Epigenetic developmental programming and intergenerational effects of thyroid hormones

Mounting evidence is showing that altered signaling through the nuclear hormone receptor superfamily can cause abnormal, long-term epigenetic changes which translate into pathological modifications and susceptibility to disease. These effects seem to be more prominent if the exposure occurs early in life, when transcriptomic profiles are rapidly changing. At this time, the coordination of the complex coordinated processes of cell proliferation and differentiation that characterize mammalian development. Such exposures may also alter the epigenetic information of the germ line, potentially leading to developmental changes and abnormal outcomes in subsequent generations. Thyroid hormone (TH) signaling is mediated by specific nuclear receptors, which have the ability to markedly change chromatin structure and gene transcription, and can also regulate other determinants of epigenetic marks. TH exhibits pleiotropic effects in mammals, and during development, its action is regulated in a highly dynamic manner to suit the rapidly evolving needs of multiple tissues. Their molecular mechanisms of action, timely developmental regulation and broad biological effects place THs in a central position to play a role in the developmental epigenetic programming of adult pathophysiology and, through effects on the germ line, in inter- and trans-generational epigenetic phenomena. These areas of epigenetic research are in their infancy, and studies regarding THs are limited. In the context of their characteristics as epigenetic modifiers and their finely tuned developmental action, here we review some of the observations underscoring the role that altered TH action may play in the developmental programming of adult traits and in the phenotypes of subsequent generations via germ line transmission of altered epigenetic information. Considering the relatively high prevalence of thyroid disease and the ability of some environmental chemicals to disrupt TH action, the epigenetic effects of abnormal levels of TH action may be important contributors to the non-genetic etiology of human disease.

IFN-γ differential expression in the hypothalamus-pituitary-ovary axis of thyroidectomized rats

IFN-γ is critical for both thyroid and ovarian function, while thyroxine, secreted from the thyroid gland, regulates the ovarian function via the hypothalamus-pituitary -ovary axis. However, the effect of thyroxine on INF-γ involved in the regulation of hypothalamic pituitary ovarian axis ovarian function is hitherto unknown. Therefore, we set up three groups including a sham-operated group, an experimental thyroidectomized group, and an experimental thyroidectomized group treated with T4 to reveal the IFN-γ expression levels in the in the hypothalamus, pituitary gland, and ovary by immunohistochemical staining, RT-PCR, and Western blotting. IFN-γ-like immunoreactive-positive substances were visualized in the hypothalamus, pituitary gland, and ovary, which were located mainly in the cytoplasm of the hypothalamic neurons anterior pituitary cells, luteal cells, and theca cells in the ovary of hypothyroidism rats, respectively. RT-PCR and Western blotting showed that the rats in the experimental thyroidectomized group treated with T4 had significantly elevated expression of IFN-γ at both the mRNA and protein levels. Thyroxine affects the expression of IFN-γ in the thalamus-pituitary-ovarian axis, which may influence the secretion of IFN-γ to regulate ovarian function during hypothyroidism. This work highlights the potential effect of thyroxine on the involvement of INF-γ in the modulation of the ovarian function in the hypothalamic-pituitary-ovarian axis.

Role of thyroid hormone in an experimental model of atherosclerosis: the potential mediating role of immune response and autophagy

Accumulating evidence has revealed that several conditions related to abnormal thyroid hormone status, such as dyslipidemia, hypertension, or hypercoagulable state, can exacerbate atherosclerotic vascular disease. Thyroid hormone effects on vascular smooth muscle cells and endothelial cells have also been studied extensively. However, only limited information is available on thyroid hormone-mediated immune response in current review articles on the pathophysiology of atherosclerosis. This report thus presents an overview of the recent advances in the understanding of the dynamic interactions taking place between thyroid hormone status and immune response in the pathogenesis of atherosclerosis. In particular, we focus on macrophages and T-lymphocytes, which have been recognized as important determinants for the initiation and development of atherosclerosis. Numerous studies have revealed the role of autophagy in immune cells produced in atherosclerosis. In addition, thyroid hormones induce autophagy in several cells and tissues, such as liver, skeletal muscles, lungs, and brown adipose tissue. Our research group, among others, have reported different targets of thyroid hormone-mediated autophagy, including lipid droplets (lipophagy), mitochondria (mitophagy), and aggregated proteins (aggrephagy). Based on these findings, thyroid hormone-mediated autophagy could serve as a novel therapeutic approach for atherosclerosis. We also consider the limitations of the current murine models for studies on atherosclerosis, especially in relation to low-density lipoprotein-cholesterol driven atherosclerotic plaque.

Thyroid Hormones Interaction With Immune Response, Inflammation and Non-thyroidal Illness Syndrome

The interdependence between thyroid hormones (THs), namely, thyroxine and triiodothyronine, and immune system is nowadays well-recognized, although not yet fully explored. Synthesis, conversion to a bioactive form, and release of THs in the circulation are events tightly supervised by the hypothalamic-pituitary-thyroid (HPT) axis. Newly synthesized THs induce leukocyte proliferation, migration, release of cytokines, and antibody production, triggering an immune response against either sterile or microbial insults. However, chronic patho-physiological alterations of the immune system, such as infection and inflammation, affect HPT axis and, as a direct consequence, THs mechanism of action. Herein, we revise the bidirectional crosstalk between THs and immune cells, required for the proper immune system feedback response among diverse circumstances. Available circulating THs do traffic in two distinct ways depending on the metabolic condition. Mechanistically, internalized THs form a stable complex with their specific receptors, which, upon direct or indirect binding to DNA, triggers a genomic response by activating transcriptional factors, such as those belonging to the Wnt/β-catenin pathway. Alternatively, THs engage integrin αvβ3 receptor on cell membrane and trigger a non-genomic response, which can also signal to the nucleus. In addition, we highlight THs-dependent inflammasome complex modulation and describe new crucial pathways involved in microRNA regulation by THs, in physiological and patho-physiological conditions, which modify the HPT axis and THs performances. Finally, we focus on the non-thyroidal illness syndrome in which the HPT axis is altered and, in turn, affects circulating levels of active THs as reported in viral infections, particularly in immunocompromised patients infected with human immunodeficiency virus.

Low-free triiodothyronine is associated with poor prognosis of portal hypertension in cirrhosis

BACKGROUND AND AIMS

The role of thyroid function in the portal hypertension development and prognosis remains unclear. This study aimed to investigate the correlation between serum-free triiodothyronine (fT3) levels and the outcomes of cirrhotic portal hypertension.

METHODS

A total of 385 cirrhotic patients with confirmed portal hypertension underwent computed tomography angiography and thyroid function test at a tertiary care referral center from January 2009 to December 2017. The patients were assigned to the low-fT3 (n = 98) and normal-fT3 groups (n = 287).

RESULTS

Child-Pugh (8.88 ± 0.22 vs. 7.09 ± 0.12, P < 0.001) and model for end-stage liver disease (MELD) scores (14.75 ± 0.57 vs. 10.59 ± 0.23, P < 0.001) significantly increased in the low-fT3 group. The hemoglobin level correlated with fT3 (R = 0.299, P < 0.0001) and fT4 (R = 0.310, P < 0.0001), while only fT3 significantly correlated with the albumin level (R = 0.537, P < 0.001). The Kaplan-Meier analysis indicated that the two-year survival rate was 74.51% in the low-fT3 group vs. 94.25% in the normal-fT3 group (P < 0.0001). The Cox regression analysis demonstrated that the serum level of fT3 [hazard ratio: 0.478; 95% confidence interval (CI) 0.391-0.758; P = 0.002] and prothrombin time (hazard ratio: 2.247; 95% CI: 1.316-3.838; P = 0.003) were independent prognostic factors in cirrhotic patients.

CONCLUSION

The low fT3 level was associated with poor prognosis and the progression of cirrhotic portal hypertension.

Nuclear Receptors as Autophagy-Based Antimicrobial Therapeutics

Autophagy is an intracellular process that targets intracellular pathogens for lysosomal degradation. Autophagy is tightly controlled at transcriptional and post-translational levels. Nuclear receptors (NRs) are a family of transcriptional factors that regulate the expression of gene sets involved in, for example, metabolic and immune homeostasis. Several NRs show promise as host-directed anti-infectives through the modulation of autophagy activities by their natural ligands or small molecules (agonists/antagonists). Here, we review the roles and mechanisms of NRs (vitamin D receptors, estrogen receptors, estrogen-related receptors, and peroxisome proliferator-activated receptors) in linking immunity and autophagy during infection. We also discuss the potential of emerging NRs (REV-ERBs, retinoic acid receptors, retinoic acid-related orphan receptors, liver X receptors, farnesoid X receptors, and thyroid hormone receptors) as candidate antimicrobials. The identification of novel roles and mechanisms for NRs will enable the development of autophagy-adjunctive therapeutics for emerging and re-emerging infectious diseases.

Multiple mechanisms regulate H3 acetylation of enhancers in response to thyroid hormone

Hormone-dependent activation of enhancers includes histone hyperacetylation and mediator recruitment. Histone hyperacetylation is mostly explained by a bimodal switch model, where histone deacetylases (HDACs) disassociate from chromatin, and histone acetyl transferases (HATs) are recruited. This model builds on decades of research on steroid receptor regulation of transcription. Yet, the general concept of the bimodal switch model has not been rigorously tested genome wide. We have used a genomics approach to study enhancer hyperacetylation by the thyroid hormone receptor (TR), described to operate as a bimodal switch. H3 acetylation, HAT and HDAC ChIP-seq analyses of livers from hypo- and hyperthyroid wildtype, TR deficient and NCOR1 disrupted mice reveal three types of thyroid hormone (T3)-regulated enhancers. One subset of enhancers is bound by HDAC3-NCOR1 in the absence of hormone and constitutively occupy TR and HATs irrespective of T3 levels, suggesting a poised enhancer state in absence of hormone. In presence of T3, HDAC3-NCOR1 dissociates from these enhancers leading to histone hyperacetylation, suggesting a histone acetylation rheostat function of HDACs at poised enhancers. Another subset of enhancers, not occupied by HDACs, is hyperacetylated in a T3-dependent manner, where TR is recruited to chromatin together with HATs. Lastly, a subset of enhancers, is not occupied directly by TR yet requires TR for histone hyperacetylation. This indirect enhancer activation involves co-association with TR bound enhancers within super-enhancers or topological associated domains. Collectively, this demonstrates various mechanisms controlling hormone-dependent transcription and adds significant details to the otherwise simple bimodal switch model.

Thyroid hormone (T3) is a central regulator of growth, thermogenesis, heart rate and metabolism. In the liver T3 binds thyroid hormone receptor beta (TRβ) controlling expression of genes involved in processes such as lipid and cholesterol metabolism. The molecular mechanisms controlling TR-dependent gene regulation are centred on a bimodal switch model. In the absence of T3 co-repressors bind TR reducing gene expression. When hormone binds TR, co-repressors dissociate, and co-activators are recruited inducing gene expression. This model predominates the current understanding of T3-regulated gene expression. However, only a few studies have tested this model by genome-wide approaches. We have quantified histone3 acetylation genome-wide in the liver of hypo- and hyperthyroid mice and identified gene regulatory regions regulated by T3. Probing TR and co-regulators at these regulatory regions, and analysing histone3 acetylation in mouse models for disrupted co-repressor and TR activity, reveal additional insights to the mechanisms regulating T3-dependent gene expression. We suggest a revision of the prevailing bimodal switch model which helps understanding T3-regulated gene expression in tissues such as liver. We hope that this study, together with future studies, will add new perspectives on nuclear receptor-mediated transcriptional regulation to reveal general principles.

Estrogen-Related Receptor Alpha: An Under-Appreciated Potential Target for the Treatment of Metabolic Diseases

The estrogen-related receptor alpha (ESRRA) is an orphan nuclear receptor (NR) that significantly influences cellular metabolism. ESRRA is predominantly expressed in metabolically-active tissues and regulates the transcription of metabolic genes, including those involved in mitochondrial turnover and autophagy. Although ESRRA activity is well-characterized in several types of cancer, recent reports suggest that it also has an important role in metabolic diseases. This minireview focuses on the regulation of cellular metabolism and function by ESRRA and its potential as a target for the treatment of metabolic disorders.

Roles of Thyroid Hormone-Associated microRNAs Affecting Oxidative Stress in Human Hepatocellular Carcinoma

Oxidative stress occurs as a result of imbalance between the generation of reactive oxygen species (ROS) and antioxidant genes in cells, causing damage to lipids, proteins, and DNA. Accumulating damage of cellular components can trigger various diseases, including metabolic syndrome and cancer. Over the past few years, the physiological significance of microRNAs (miRNA) in cancer has been a focus of comprehensive research. In view of the extensive level of miRNA interference in biological processes, the roles of miRNAs in oxidative stress and their relevance in physiological processes have recently become a subject of interest. In-depth research is underway to specifically address the direct or indirect relationships of oxidative stress-induced miRNAs in liver cancer and the potential involvement of the thyroid hormone in these processes. While studies on thyroid hormone in liver cancer are abundantly documented, no conclusive information on the potential relationships among thyroid hormone, specific miRNAs, and oxidative stress in liver cancer is available. In this review, we discuss the effects of thyroid hormone on oxidative stress-related miRNAs that potentially have a positive or negative impact on liver cancer. Additionally, supporting evidence from clinical and animal experiments is provided.

Thyroxine Affects Lipopolysaccharide-Induced Macrophage Differentiation and Myocardial Cell Apoptosis via the NF-κB p65 Pathway Both In Vitro and In Vivo

Background

Numerous studies have demonstrated that the inflammatory response is involved in the progression of lipopolysaccharide- (LPS-) induced myocardial cell apoptosis. Accumulating evidence has shown that thyroxine participates in diseases by downregulating the inflammatory response. This study aimed at investigating whether thyroxine alleviates LPS-induced myocardial cell apoptosis.

Methods

Bone marrow-derived macrophages (Mø) were treated with LPS and thyroxine, and Mø differentiation and Mø-related cytokine expression were measured. The effect of Mø differentiation on mouse cardiomyocyte (MCM) apoptosis was also detected in vitro. In addition, C57BL/6 mice underwent thyroidectomy and were treated with LPS 35 days later; subsequently, Mø differentiation and myocardial cell apoptosis in hearts were analyzed. To determine whether the nuclear factor-kappa B (NF-κB) p65 pathway mediates the effect of thyroxine on Mø differentiation and myocardial cell apoptosis, the specific NF-κB p65 pathway inhibitor JSH-23 was administered to mice that underwent a thyroidectomy.

Results

Levothyroxine treatment significantly reduced the activation of the NF-κB p65 pathway, decreased M1 macrophage (Mø1) differentiation and Mø1-related cytokine mRNA levels in LPS-treated Mø, and increased M2 macrophage (Mø2) differentiation and Mø2-related cytokine mRNA expression. The protective effects of levothyroxine on MCM apoptosis mediated by LPS-treated Mø were alleviated by JSH-23. In mice, thyroidectomy aggravated LPS-induced cardiac injury and cardiac dysfunction, further promoted NF-κB p65 activation, and increased cardiac Mø1 expression and myocardial cell apoptosis but decreased cardiac Mø2 expression. JSH-23 treatment significantly ameliorated the thyroidectomy-induced increases in myocardial cell apoptosis and Mø differentiation.

Conclusions

Thyroxine alleviated the Mø1/Mø2 imbalance, reduced the inflammatory response, decreased myocardial cell apoptosis, and protected against cardiac injury and cardiac dysfunction in LPS-treated mice. Thyroxine may be a novel therapeutic strategy to prevent and treat LPS-induced cardiac injury.

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

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

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

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

miRNA-125a modulates autophagy of thyroiditis through PI3K/Akt/mTOR signaling pathway

The present study examined the potential function and underlying mechanisms of microRNA-125a (miR-125a) in thyroiditis. Mice were subcutaneously administered with 100 µg porcine thyroglobulin weekly for 2 weeks to establish the thyroiditis model. Results of the in vivo study demonstrated that miR-125a serum expression was upregulated in thyroiditis mice compared with the control group. In vitro studies were performed on a mouse macrophage cell line in which a model of thyroiditis was established using 10 ng/ml human interferon-γ. Upregulated miR-125a expression was achieved via mimic transfection. Increased miR-125a expression reduced autophagy and cell proliferation, increased the apoptotic rate and the expression of pro-inflammatory factors tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-18 via downregulation of the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway. PI3K inhibition enhanced the ability of miR-125a to increase the inflammatory response in vitro via regulation of the PI3K/Akt/mTOR signaling pathway. These results suggest miR-125a inhibited autophagy in a model of thyroiditis through the PI3K/Akt/mTOR signaling pathway.

Novel Insight Into the Epigenetic and Post-transcriptional Control of Cardiac Gene Expression by Thyroid Hormone

Thyroid hormone (TH) signaling is critically involved in the regulation of cardiovascular physiology. Even mild reductions of myocardial TH levels, as occur in hypothyroidism or low T3 state conditions, are thought to play a role in the progression of cardiac disorders. Due to recent advances in molecular mechanisms underlying TH action, it is now accepted that TH-dependent modulation of gene expression is achieved at multiple transcriptional and post-transcriptional levels and involves the cooperation of many processes. Among them, the epigenetic remodeling of chromatin structure and the interplay with non-coding RNA have emerged as novel TH-dependent pathways that add further degrees of complexity and broaden the network of genes controlled by TH signaling. Increasing experimental and clinical findings indicate that aberrant function of these regulatory mechanisms promotes the evolution of cardiac disorders such as post-ischemic injury, pathological hypertrophy, and heart failure, which may be reversed by the correction of the underlying TH dyshomeostasis. To encourage the clinical implementation of a TH replacement strategy in cardiac disease, here we discuss the crucial effect of epigenetic modifications and control of non-coding RNA in TH-dependent regulation of biological processes relevant for cardiac disease evolution.

Novel Transcriptional Mechanisms for Regulating Metabolism by Thyroid Hormone

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

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.

Restoration of type 1 iodothyronine deiodinase expression in renal cancer cells downregulates oncoproteins and affects key metabolic pathways as well as anti-oxidative system

Type 1 iodothyronine deiodinase (DIO1) contributes to deiodination of 3,5,3’,5’-tetraiodo-L-thyronine (thyroxine, T4) yielding of 3,5,3’-triiodothyronine (T3), a powerful regulator of cell differentiation, proliferation, and metabolism. Our previous work showed that loss of DIO1 enhances proliferation and migration of renal cancer cells. However, the global effects of DIO1 expression in various tissues affected by cancer remain unknown. Here, the effects of stable DIO1 re-expression were analyzed on the proteome of renal cancer cells, followed by quantitative real-time PCR validation in two renal cancer-derived cell lines. DIO1-induced changes in intracellular concentrations of thyroid hormones were quantified by L-MS/MS and correlations between expression of DIO1 and potential target genes were determined in tissue samples from renal cancer patients. Stable re-expression of DIO1, resulted in 26 downregulated proteins while 59 proteins were overexpressed in renal cancer cells. The ‘downregulated’ group consisted mainly of oncoproteins (e.g. STAT3, ANPEP, TGFBI, TGM2) that promote proliferation, migration and invasion. Furthermore, DIO1 re-expression enhanced concentrations of two subunits of thyroid hormone transporter (SLC7A5, SLC3A2), enzymes of key pathways of cellular energy metabolism (e.g. TKT, NAMPT, IDH2), sex steroid metabolism and anti-oxidative response (AKR1C2, AKR1B10). DIO1 expression resulted in elevated intracellular concentration of T4. Expression of DIO1-affected genes strongly correlated with DIO1 transcript levels in tissue samples from renal cancer patients as well as with their poor survival. This first study addressing effects of deiodinase re-expression on proteome of cancer cells demonstrates that induced DIO1 re-expression in renal cancer robustly downregulates oncoproteins, affects key metabolic pathways, and triggers proteins involved in anti-oxidative protection. This data supports the notion that suppressed DIO1 expression and changes in local availability of thyroid hormones might favor a shift from a differentiated to a more proliferation-prone state of cancer tissues and cell lines.