New insights into thyroid hormone action

Medium-Chain Chlorinated Paraffins Trigger Thyroid Hormone Synthesis and Interfere with Mitochondrial Function in the Thyroid Gland

Medium-chain chlorinated paraffins (MCCPs, C14-C17) are frequently detected in diverse environmental media. It has been proposed to be listed in Annex A of the Convention on Persistent Organic Pollutants in 2023. Although MCCPs are a crucial health concern, their toxicity remains unclear. This study investigated the toxic effects of MCCPs (0.1-50 mg/kg body weight/day) on the thyroid gland of female Sprague-Dawley rats and characterized the potential toxic pathways via transcriptomics and metabolomics approaches. MCCPs exposure caused histopathological changes to the endoplasmic reticula and mitochondria in thyroid follicular cells at a dose of 50 mg/kg bw/d and increased serum thyrotropin-releasing hormone, thyroid-stimulating hormones, and thyroxine when exposed to a higher dose of MCCPs. Transcriptomic analysis indicated the excessive expression of key genes related to thyroid hormone synthesis induced by MCCPs. Integrating the dual-omics analysis revealed mitochondrial dysfunction of the thyroid by mediating fatty acid oxidation, Kreb's cycle, and oxidative phosphorylation. Significant metabolic toxicity on the thyroid might be linked to the characteristics of the chlorine content of MCCPs. This study revealed the toxicity of MCCPs to the thyroid gland via triggering thyroid hormone synthesis and interfering with mitochondrial function, which can provide new insights into the modes of action and mechanism-based risk assessment of MCCPs.

Extreme temperatures, PM2.5 and trajectories of impaired thyroid hormone sensitivity: A longitudinal study of patients with schizophrenia

BACKGROUND

The climate change scenario has witnessed an increase in extreme temperature events (ETEs), including heat waves and cold spells, and a heightened occurrence of compounding with fine particulate matter (PM2.5). However, the impact of this phenomenon on the sensitivity to thyroid hormones (THs) in humans is unclear, especially in a group as specific as schizophrenia.

METHODS

A longitudinal study was constructed using longitudinal measurements of thyroid function in schizophrenia in the Anhui Mental Health Center. The latent growth mixture model was applied to assess the optimal trajectory of change in impaired THs sensitivity. We then used logistic regression to explore associations between heat waves, cold spells, and PM2.5 with impaired THs sensitivity trajectories in the total population and different gender and age subgroups. Furthermore, the effect of the frequency, intensity, and duration of ETEs in the above associations was explored, as well as an assessment of the interaction between ETEs and PM2.5.

RESULTS

Among 931 participants, we identified two classifications of trajectories of impaired THs sensitivity: "Low-stable" (n = 836, 89.80 %) and "Rise-slight down" (n = 95, 10.20 %). Logistic regression showed significant associations between each additional day of heat waves (≥3 days with temperature thresholds above the 95th percentile) and cold spells (≥3 days with temperature thresholds below the 5th percentile) and "Rise-slight down" trajectory, with odds ratios (95 % confidence intervals) of 1.06 (1.02, 1.10) and 1.19 (1.14, 1.24), respectively, and the strength of this association increased with the intensity and duration of ETEs. Subgroup analyses indicated that the association was more pronounced in males and the age group above 40 years. Furthermore, PM2.5 was found to interact with heat waves, with high concentrations exacerbating the effects of heat waves.

CONCLUSIONS

Our findings suggest that mitigating both ETEs and PM2.5 exposures may bring health co-benefits in preventing thyroid impairment in schizophrenia.

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.

Evaluation of Health-Related Quality of Life in Patients with Euthyroid Hashimoto's Thyroiditis under Long-Term Levothyroxine Therapy: A Prospective Case-Control Study

Objectives: To investigate quality of life using the SF-12 scale in euthyroid Hashimoto's thyroiditis patients on levothyroxine therapy for at least three years. Methods: This prospective case-control study included 44 euthyroid Hashimoto's thyroiditis patients and 44 matched controls, conducted at a university hospital's endocrinology clinic from 6 November to 30 December 2023. Participants completed the SF-12 questionnaire; data were analyzed using Shapiro-Wilk, Student's t-test, Mann-Whitney U, Yates chi-squared, and Spearman's tests. Results: The study involved 88 participants (Hashimoto's group: 35 females, 9 males; control group: 31 females, 13 males), with average ages of 49.50 and 47.43 years old, respectively. Significant differences were observed in TSH, T4 levels, and family history (p < 0.05). The Hashimoto's thyroiditis group showed higher thyroid peroxidase antibodies (95.69 IU/mL) and lower scores on both physical and mental sub-dimensions of SF-12, with a significant difference in physical scores (p < 0.05). Significant correlations were found between age and Anti-TG; Anti-TPO and Anti-TG; BMI and T3; TSH and T4; HDL and triglycerides; MCS-12 and PCS-12; Anti-TPO and T3; cholesterol and T3; and LDL and cholesterol (p < 0.05). Other variables showed no significant correlations (p > 0.05). Conclusions: Our study shows that effective control of hypothyroidism is not sufficient to reduce the negative effects of Hashimoto's thyroiditis on patients' health-related quality of life. Beyond the normalization of hormone levels, comprehensive therapeutic strategies targeting the autoimmune aspects of the disease are essential for the management of Hashimoto's thyroiditis. This study provides a foundation for developing effective therapies that can enhance quality of life for patients with Hashimoto's thyroiditis.

Microstructural alterations of the hypothalamus in Parkinson's disease and probable REM sleep behavior disorder

BACKGROUND

Whether there is hypothalamic degeneration in Parkinson's disease (PD) and its association with clinical symptoms and pathophysiological changes remains controversial.

OBJECTIVES

We aimed to quantify microstructural changes in hypothalamus using a novel deep learning-based tool in patients with PD and those with probable rapid-eye-movement sleep behavior disorder (pRBD). We further assessed whether these microstructural changes associated with clinical symptoms and free thyroxine (FT4) levels.

METHODS

This study included 186 PD, 67 pRBD, and 179 healthy controls. Multi-shell diffusion MRI were scanned and mean kurtosis (MK) in hypothalamic subunits were calculated. Participants were assessed using Unified Parkinson's Disease Rating Scale (UPDRS), RBD Questionnaire-Hong Kong (RBDQ-HK), Hamilton Depression Rating Scale (HAMD), and Activity of Daily Living (ADL) Scale. Additionally, a subgroup of PD (n = 31) underwent assessment of FT4.

RESULTS

PD showed significant decreases of MK in anterior-superior (a-sHyp), anterior-inferior (a-iHyp), superior tubular (supTub), and inferior tubular hypothalamus when compared with healthy controls. Similarly, pRBD exhibited decreases of MK in a-iHyp and supTub. In PD group, MK in above four subunits were significantly correlated with UPDRS-I, HAMD, and ADL. Moreover, MK in a-iHyp and a-sHyp were significantly correlated with FT4 level. In pRBD group, correlations were observed between MK in a-iHyp and UPDRS-I.

CONCLUSIONS

Our study reveals that microstructural changes in the hypothalamus are already significant at the early neurodegenerative stage. These changes are associated with emotional alterations, daily activity levels, and thyroid hormone levels.

Thyroid Hormone Receptor Agonistic and Antagonistic Activity of Newly Synthesized Dihydroxylated Polybrominated Diphenyl Ethers: An In Vitro and In Silico Coactivator Recruitment Study

Dihydroxylated polybrominated diphenyl ethers (DiOH-PBDEs) could be the metabolites of PBDEs of some organisms or the natural products of certain marine bacteria and algae. OH-PBDEs may demonstrate binding affinity to thyroid hormone receptors (TRs) and can disrupt the functioning of the systems modulated by TRs. However, the thyroid hormone disruption mechanism of diOH-PBDEs remains elusive due to the absence of diOH-PBDEs standards. This investigation explores the potential disruptive effects of OH/diOH-PBDEs on thyroid hormones via competitive binding and coactivator recruitment with TRα and TRβ. At levels of 5000 nM and 25,000 nM, 6-OH-BDE-47 demonstrated significant recruitment of steroid receptor coactivator (SRC), whereas none of the diOH-PBDEs exhibited SRC recruitment within the range of 0.32-25,000 nM. AutoDock CrankPep (ADCP) simulations suggest that the conformation of SRC and TR-ligand complexes, particularly their interaction with Helix 12, rather than binding affinity, plays a pivotal role in ligand agonistic activity. 6,6'-diOH-BDE-47 displayed antagonistic activity towards both TRα and TRβ, while the antagonism of 3,5-diOH-BDE-100 for TRα and TRβ was concentration-dependent. 3,5-diOH-BDE-17 and 3,5-diOH-BDE-51 exhibited no discernible agonistic or antagonistic activities. Molecular docking analysis revealed that the binding energy of 3,3',5-triiodo-L-thyronine (T3) surpassed that of OH/diOH-PBDEs. 3,5-diOH-BDE-100 exhibited the highest binding energy, whereas 6,6'-diOH-BDE-47 displayed the lowest. These findings suggest that the structural determinants influencing the agonistic and antagonistic activities of halogen phenols may be more intricate than previously proposed, involving factors beyond high-brominated PBDEs or hydroxyl group and bromine substitutions. It is likely that the agonistic or antagonistic propensities of OH/diOH-PBDEs are instigated by protein conformational changes rather than considerations of binding energy.

Low T3 syndrome as a predictor of poor prognosis in peripheral T-cell lymphomas

PURPOSE

The purpose of the study was to evaluate the prognostic value of low T3 syndrome in peripheral T-cell lymphomas (PTCLs).

METHODS

One hundred and seventy-four patients of newly diagnosed PTCLs were enrolled in the study. We performed statistical analysis based on the clinical data collected.

RESULTS

Thirty-Six (20.69%) patients had low T3 syndrome at first admission. Results suggested that the patients with higher score of ECOG PS, International Prognostic Index (IPI) and Prognostic Index for T-cell lymphoma (PIT), bone marrow involvement and lower level of albumin tended to develop low T3 syndrome. The median progression-free survival (PFS) and overall survival (OS) were 10 months and 36 months, respectively, for all patients. Pre-existing low T3 syndrome was in correlation with worse PFS and OS. Patients with low T3 syndrome showed worse PFS (4 months vs 13 months, P = 0.0001) and OS (7 months vs 83 months, P < 0.0001) than patients without low T3 syndrome. IPI and PIT, respectively, combined with low T3 syndrome improved the ability to predict OS and PFS of PTCLs.

CONCLUSIONS

The study indicated that low T3 syndrome may be a good candidate for predicting prognosis of peripheral T-cell lymphomas.

Photoperiod and metabolic health: evidence, mechanism, and implications

Circadian rhythms are evolutionarily programmed biological rhythms that are primarily entrained by the light cycle. Disruption of circadian rhythms is an important risk factor for several metabolic disorders. Photoperiod is defined as total duration of light exposure in a day. With the extended use of indoor/outdoor light, smartphones, television, computers, and social jetlag people are exposed to excessive artificial light at night increasing their photoperiod. Importantly long photoperiod is not limited to any geographical region, season, age, or socioeconomic group, it is pervasive. Long photoperiod is an established disrupter of the circadian rhythm and can induce a range of chronic health conditions including adiposity, altered hormonal signaling and metabolism, premature ageing, and poor psychological health. This review discusses the impact of exposure to long photoperiod on circadian rhythms, metabolic and mental health, hormonal signaling, and ageing and provides a perspective on possible preventive and therapeutic approaches for this pervasive challenge.

The Differential Effect of a Shortage of Thyroid Hormone Compared with Knockout of Thyroid Hormone Transporters Mct8 and Mct10 on Murine Macrophage Polarization

Innate immune cells, including macrophages, are functionally affected by thyroid hormone (TH). Macrophages can undergo phenotypical alterations, shifting between proinflammatory (M1) and immunomodulatory (M2) profiles. Cellular TH concentrations are, among others, determined by TH transporters. To study the effect of TH and TH transporters on macrophage polarization, specific proinflammatory and immunomodulatory markers were analyzed in bone marrow-derived macrophages (BMDMs) depleted of triiodothyronine (T3) and BMDMs with a knockout (KO) of Mct8 and Mct10 and a double KO (dKO) of Mct10/Mct8. Our findings show that T3 is important for M1 polarization, while a lack of T3 stimulates M2 polarization. Mct8 KO BMDMs are unaffected in their T3 responsiveness, but exhibit slight alterations in M2 polarization, while Mct10 KO BMDMs show reduced T3 responsiveness, but unaltered polarization markers. KO of both the Mct8 and Mct10 transporters decreased T3 availability and, contrary to the T3-depleted BMDMs, showed partially increased M1 markers and unaltered M2 markers. These data suggest a role for TH transporters besides transport of TH in BMDMs. This study highlights the complex role of TH transporters in macrophages and provides a new angle on the interaction between the endocrine and immune systems.

Assessment of Individual and Mixed Effects of Six Minerals on Thyroid Hormones in Chinese Pregnant Women

The biosynthesis of thyroid hormones is essential for brain and neurological development. It requires iodine as a key component but is also influenced by other nutrients. Evidence for the combined nutrient status in relation to thyroid hormones during pregnancy is limited. We aimed to investigate the joint associations of iodine, selenium, zinc, calcium, magnesium and iron with maternal thyroid functions in 489 pregnant women from Hangzhou, China. Serum levels of six essential minerals and thyroid function parameters were measured during the first antenatal visit. Linear regression, quantile g-computation and Bayesian kernel machine regression were used to explore the individual and joint relationships between the six minerals and thyroid hormones. Linear regression analyses revealed that calcium was positively associated with free triiodothyronine (FT3). Zinc was positively associated with free thyroxine (FT4). Iodine was negatively associated with thyroid-stimulating hormone (TSH) and positively associated with FT3 and FT4. The quantile g-computation and BKMR models indicated that the joint nutrient concentration was negatively associated with TSH and positively associated with FT3 and FT4. Among the six minerals, iodine contributed most to thyroid function. The findings suggested that maintaining the appropriate concentration of minerals, either as individuals or a mixture, is important for thyroid health during pregnancy.

Structure-Related Thyroid Disrupting Effect of Perfluorooctanesulfonate-like Substances in Zebrafish Larvae

Chlorinated polyfluorooctane ether sulfonate (6:2 Cl-PFESA), hydrogenated polyfluorooctane ether sulfonate (6:2 H-PFESA), and chlorinated polyfluorooctanesulfonate (Cl-PFOS) share structural similarities with the regulated perfluorooctanesulfonate (PFOS), but their toxic potential is rarely known. Here, the thyroid disrupting potential of these four compounds in zebrafish larvae has been comparably investigated. PFOS, Cl-PFOS, and 6:2 Cl-PFESA were accumulated in the larvae at similar levels, approximately 1.3-1.6 times higher than 6:2 H-PFESA. Additionally, PFOS, Cl-PFOS, and 6:2 Cl-PFESA exhibited stronger disruption than 6:2 H-PFESA on genetic regulation, particularly concerning thyroid hormone (TH) activation and action and on TH homeostasis in both free and total forms of thyroxine (T4) and 3,5,3'-triiodothyronine (T3). These results indicate that chlorination or oxygen insertion does not substantially alter the thyrotoxicity of PFOS, but hydrogenation mitigates it. Molecular docking analysis and the luciferase reporter gene assay provided mechanistic perspectives that the PFOS-like substances could competitively replace THs to bind with TH plasma and membrane transporters, thereby disrupting TH transport and action, respectively. Moreover, they are also potent to disrupt TH synthesis and activation through Na+/K+-dependent transport of I- or competitive binding to the sites of deiodinases.

Thyroid hormone receptor alpha modulates fibrogenesis in hepatic stellate cells

OBJECTIVE

Progressive hepatic fibrosis can be considered the final stage of chronic liver disease. Hepatic stellate cells (HSC) play a central role in liver fibrogenesis. Thyroid hormones (TH, e.g. thyroxine; T4 and triiodothyronine; T3) significantly affect development, growth, cell differentiation and metabolism through activation of TH receptor α and/or β (TRα/β). Here, we evaluated the influence of TH in hepatic fibrogenesis.

DESIGN

Human liver tissue was obtained from explanted livers following transplantation. TRα-deficient (TRα-KO) and wild-type (WT) mice were fed a control or a profibrogenic methionine-choline deficient (MCD) diet. Liver tissue was assessed by qRT-PCR for fibrogenic gene expression. In vitro, HSC were treated with TGFβ in the presence or absence of T3. HSC with stable TRα knockdown and TRα deficient mouse embryonic fibroblasts (MEF) were used to determine receptor-specific function. Activation of HSC and MEF was assessed using the wound healing assay, Western blotting, and qRT-PCR.

RESULTS

TRα and TRβ expression is downregulated in the liver during hepatic fibrogenesis in humans and mice. TRα represents the dominant isoform in HSC. In vitro, T3 blunted TGFβ-induced expression of fibrogenic genes in HSC and abrogated wound healing by modulating TGFβ signalling, which depended on TRα presence. In vivo, TRα-KO enhanced MCD diet-induced liver fibrogenesis.

CONCLUSION

These observations indicate that TH action in non-parenchymal cells is highly relevant. The interaction of TRα with TH regulates the phenotype of HSC via the TGFβ signalling pathway. Thus, the TH-TR axis may be a valuable target for future therapy of liver fibrosis.

Association between ambient air pollution and thyroid hormones levels: A systematic review and meta-analysis

BACKGROUND

Growing studies have focused on the effects of ambient air pollution on thyroid hormones (THs), but the results were controversial. Therefore, a systematic review and meta-analysis was conducted by pooling current evidence on this association.

METHODS

Four databases were searched for studies examining the associations of particulate matter [diameter ≤10 μm (PM10) or ≤2.5 μm (PM2.5)] and gaseous [sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO)] pollutants with THs levels. Random effects models were used to pool the changes in THs levels with increasing air pollutant concentrations. Subgroup analyses were constructed by region, design, sample size, pollutant concentrations, evaluated methods, and potential risk exposure windows.

RESULTS

A total of 14 studies covering 357,226 participants were included in this meta-analysis. The pooled results showed significant associations of exposure to PM2.5, PM10, NO2, SO2, and CO with decreases in free thyroxine (FT4) with percent changes (PC) ranging from -0.593 % to -3.925 %. PM2.5, NO2, and CO were negatively associated with levels of FT4/FT3 (PC: from -0.604 % to -2.975 %). In addition, results showed significant associations of PM2.5 with hypothyroxinemia and high thyroid-stimulating hormone (TSH). Subgroup analyses indicated that PM2.5 and NO2 were significantly associated with FT4 in studies of Chinese, and similar significant findings were found in studies of PM2.5 and FT4/FT3 in areas with higher concentrations of air pollutants and larger samples. PM2.5 exposure in the first trimester was found to be associated with lower FT4 levels in pregnant women.

CONCLUSION

Our findings suggest that exposure to air pollution is associated with changes in THs levels. Enhanced management of highly polluted areas, identification of harmful components and sources of PM, and protection from harmful exposures in early pregnancy may be of great public health importance for the population's thyroid function.

Prevalence and Trends of Thyroid Disease Among Adults, 1999-2018

BACKGROUND

Thyroid disease is a prominent endocrine disorder, yet the clinical epidemiology of this condition remains unclear. This study aims to describe the recent trends in the prevalence of thyroid disease in US adults from 1999-2018.

METHODS

This cross-sectional study used nationally representative data collected through the National Health and Nutrition Examination Survey (NHANES) from January 1, 1999 to December 31, 2018. Patients with thyroid disease were defined as patients who reported having a thyroid disease and were on thyroid-related treatment. Age-standardized prevalence of thyroid disease was calculated within 4-year survey periods (1999-2002, 2003-2006, 2007-2010, 2011-2014, and 2015-2018).

RESULTS

During the NHANES 1999-2018, a total of 57 540 participants were examined. The age-standardized prevalence of thyroid disease was 5.05% (95% CI, 4.55%-5.60%) from 2015-2018, signifying a significant increase from the 1999-2002 period (P <.0002). However, prevalent thyroid disease remained steady between 2003 and 2014. The highest prevalence of thyroid disease was observed in non-Hispanic Whites (8.1%; 95% CI, 7.3%-9.0%), individuals aged ≥60 years (15.4%; 95% CI, 13.3%-17.8%), and tended to be higher in women (7.6%; 95% CI, 6.8%-8.5%). Multiple regression analysis revealed that age, women sex, non-Hispanic White and Mexican American, body mass index, higher education and incomes were independently associated with increased risks of thyroid disease.

CONCLUSION

The age-standardized prevalence of thyroid disease among US adults increased from 1999-2003, remained stable between 2003 and 2014, and then saw an increase from 2014-2018, with the highest rate observed among elders, women, and non-Hispanic Whites.

The role of the thyroid in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine and metabolic disease in women of childbearing age and can cause metabolic disorder, infertility, and increased anxiety and depression; as a result, it can seriously affect the physical and mental health of fertile women. PCOS is a highly clinically heterogeneous disease with unclear etiology and pathogenesis, which increases the difficulty of treatment. The thyroid gland has complex regulatory effects on metabolism, reproduction, and emotion, and produces hormones that act on almost all cells of the human body. The clinical manifestations of PCOS are similar to some thyroid diseases. Furthermore, some thyroid diseases, such as subclinical hypothyroidism (SCH), not only increase the incidence rate of PCOS, but also exacerbate its associated metabolic abnormalities and reproductive disorders. Interestingly, PCOS also increases the incidence of some thyroid diseases. However, the role of the thyroid in PCOS remains unclear. This review is intended to thoroughly explore the critical role of the thyroid in PCOS by summarizing the comorbidity of PCOS and thyroid diseases and their combined role in metabolic disorders, related metabolic diseases, and reproductive disorders; and by analyzing the potential mechanism through which the thyroid influences the development and progression of PCOS and its symptoms. We hope this review will provide a valuable reference for the role of the thyroid in PCOS.

A Historical Reflection on Scientific Advances in Understanding Thyroid Hormone Action

Background: Thyroid hormone (TH) has actions in every tissue of the body and is essential for normal development, as well as having important actions in the adult. The earliest markers of TH action that were identified and monitored clinically, even before TH could be measured in serum, included oxygen consumption, basal metabolic rate, serum cholesterol, and deep tendon reflex time. Cellular, rodent, amphibian, zebrafish, and human models have been used to study TH action. Summary: Early studies of the mechanism of TH action focused on saturable-specific triiodothyronine (T3) nuclear binding and direct actions of T3 that altered protein expression. Additional effects of TH were recognized on mitochondria, stimulation of ion transport, especially the sodium potassium ATPase, augmentation of adrenergic signaling, role as a neurotransmitter, and direct plasma membrane effects. The cloning of the thyroid hormone receptor (THR) genes in 1986 and report of the THR crystal structure in 1995 produced rapid progress in understanding the mechanism of TH nuclear action, as well as the development of modified THR ligands. These findings revealed nuances of TH signaling, including the role of nuclear receptor coactivators and corepressors, repression of positively stimulated genes by the unliganded receptor, THR isoform-specific actions of TRα (THRA) and TRβ (THRB), and THR binding DNA as a heterodimer with retinoid-x-receptor (RXR) for genes positively regulated by TH. The identification of genetic disorders of TH transport and signaling, especially Resistance to Thyroid Hormone (RTH) and monocarboxylate transporter 8 (Mct8) defects, has been highly informative with respect to the mechanism of TH action. Conclusions: The impact of THR isoform, post-translational modifications, receptor cofactors, DNA response element, and selective TH tissue uptake, on TH action, have clinical implications for diagnosing and treating thyroid disease. Additionally, these findings have led to the development of novel TH and TH analogue therapies for metabolic, neurological, and cardiovascular diseases.

Thyroid hormone receptor α1: a novel regulator of thyroid cancer cell differentiation

Thyroid hormone receptor α1 (TRα1) mediates the genomic actions of thyroid hormone (T3). The biology of TRα1 in growth and development has been well studied, but the functional role of TRα1 in cancers remains to be elucidated. Analysis of the human thyroid cancer database of The Cancer Genome Atlas (TCGA) showed that THRA gene expression is lost in highly dedifferentiated anaplastic thyroid cancer (ATC). We, therefore, explored the effects of TRα1 on the progression of ATC. We stably expressed TRα1 in two human ATC cell lines, THJ-11T (11T-TRα1 #2, #7, and #8) and THJ-16T (16T-TRα1 #3, #4, and #8) cells. We found that the expressed TRα1 inhibited ATC cell proliferation and induced apoptosis. TCGA data showed that THRA gene expression was best correlated with the paired box gene 8 (PAX8). Consistently, we found that the PAX8 expression was barely detectable in parental 11T and 16T cells. However, PAX8 gene expression was elevated in 11T- and 16T-TRα1-expressing cells at the mRNA and protein levels. Using various molecular analyses, we found that TRα1 directly regulated the expression of the PAX8 gene. Single-cell transcriptomic analyses (scRNA-seq) demonstrated that TRα1 functions as a transcription factor through multiple signaling pathways to suppress tumor growth. Importantly, scRNA-seq analysis showed that TRα1-induced PAX8, via its transcription program, shifts the cell landscape of ATC toward a differentiated state. The present studies suggest that TRα1 is a newly identified regulator of thyroid differentiation and could be considered as a potential therapeutic target to improve the outcome of ATC patients.

Deiodinase Types 1 and 3 and Proinflammatory Cytokine Values May Discriminate Depressive Disorder Patients from Healthy Controls

INTRODUCTION

Depressive disorders are multifactorial diseases in that a variety of factors may play a role in their etiology, including inflammation and abnormalities in the thyroid hormone (TH) metabolism and levels. The purpose of this study was to evaluate iodothyronine deiodinases (DIOs) and DIO-interacting cytokines as possible biomarkers in the diagnosis of depressive disorders.

METHODS

This study enrolled 73 patients diagnosed with recurrent depressive disorder (rDD) and 54 controls. The expressions of DIO1, DIO2, DIO3, IL1B, IL6, TNFA, and IFNG genes, encoding three types of DIOs (1, 2, and 3), interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ, were assessed using the polymerase chain reaction in blood cells and an enzymatic immunoassay method in serum. The levels of examined molecules between patients and controls were compared, and correlations and diagnostic values were evaluated.

RESULTS

Lower levels of DIO2 and higher levels of IL1B, IL6, and TNFA were found in patients compared to controls. The protein concentrations of DIO1 and DIO2 were lower, while that of DIO3 was higher, in patients than in controls. Serum IL-1β, IL-6, and TNF-α were also higher in patients than in controls. The area under the curve (AUC) of the IL-1β, IL-6, DIO1, and DIO3 proteins was >0.7 for discriminating patients with rDD from controls.

CONCLUSIONS

The expressions of genes for DIO2, IL-1β, IL-6, and TNF-α may have a role in the estimation of processes present in depressive disorders. We can cautiously claim that DIO1 and DIO3 and pivotal cytokines, mainly IL-1β and IL-6, may play a role in depression diagnosis, and further studies are suggested to explain the exact role of these molecules in larger samples with more precise methods.

Transcriptome profiling in rumen, reticulum, omasum, and abomasum tissues during the developmental transition of pre-ruminant to the ruminant in yaks

The development of the four stomachs of yak is closely related to its health and performance, however the underlying molecular mechanisms are largely unknown. Here, we systematically analyzed mRNAs of four stomachs in five growth time points [0 day, 20 days, 60 days, 15 months and 3 years (adult)] of yaks. Overall, the expression patterns of DEmRNAs were unique at 0 d, similar at 20 d and 60 d, and similar at 15 m and adult in four stomachs. The expression pattern in abomasum was markedly different from that in rumen, reticulum and omasum. Short Time-series Expression Miner (STEM) analysis demonstrated that multi-model spectra are drastically enriched over time in four stomachs. All the identified mRNAs in rumen, reticulum, omasum and abomasum were classified into 6, 4, 7, and 5 cluster profiles, respectively. Modules 9, 38, and 41 were the most significant three colored modules. By weighted gene co-expression network analysis (WGCNA), a total of 5,486 genes were categorized into 10 modules. CCKBR, KCNQ1, FER1L6, and A4GNT were the hub genes of the turquoise module, and PAK6, TRIM29, ADGRF4, TGM1, and TMEM79 were the hub genes of the blue module. Furthermore, functional KEGG enrichment analysis suggested that the turquoise module was involved in gastric acid secretion, sphingolipid metabolism, ether lipid metabolism, etc., and the blue module was enriched in pancreatic secretion, pantothenate and CoA biosynthesis, and starch and sucrose metabolism, etc. Our study aims to lay a molecular basis for the study of the physiological functions of rumen, reticulum, omasum and abomasum in yaks. It can further elucidate the important roles of these mRNAs in regulation of growth, development and metabolism in yaks, and to provide a theoretical basis for age-appropriate weaning and supplementary feeding in yaks.

The relationship between sleep duration and thyroid function in the adult US population: NHANES 2007-2012

OBJECTIVE

Sleep disturbance is a common problem in the general population. Sleep deprivation or dysfunction can have profound health consequences. However, how sleep duration is associated with thyroid function remains unclear. This study was thus developed to examine the association between sleep duration and thyroid function in the US adult population.

METHODS

A total of 8102 participants from the NHANES 2007-2012 dataset were included in this study. Weighted data analyses were conducted, and the link between sleep duration and thyroid function was probed using linear regression models with smoothed curve fitting. Stratified analyses were also performed.

RESULTS

Weighted mean (standard deviation) values for study variables were as follows: sleep duration 6.85 (0.02) hours, thyroid-stimulating hormone (TSH) 1.86 (0.03) mIU/ml, serum free T3 3.20 (0. 01) pg/mL, serum free T4 0.80 (0.01) ng/dL, serum total T3 115.12 (0.64) ng/dL, serum total T4 7.81 (0.04) ug/dL, TPOAb 16.20 (1.53) IU/mL, TgAb 5.75 (0.73) IU/mL, and Tg 15.11 (0.46) ng/mL. In unadjusted analyses, increased sleep duration was associated with higher serum TSH levels and decreased FT3 levels. After adjustment for potential confounders, a significant negative relationship was detected between sleep duration and FT3 levels in participants with ≤7 hours of sleep. When sleep duration exceeded 7 hours, no significant changes in FT3 levels were observed after further increases in sleep duration.

CONCLUSION

Increased sleep duration was related to decreased FT3 levels, primarily at short sleep durations, and this correlation was no longer evident when participants reached the recommended healthy sleep duration.

The Impact of Metformin on the Development of Hypothyroidism and Cardiotoxicity Induced by Cyclophosphamide, Methotrexate, and Fluorouracil in Rats

Cyclophosphamide (CYP), methotrexate (MTX), and 5-fluorouracil (5-FU) are extensively utilized in the therapeutic management of various malignancies. It is noteworthy, however, that potential chemotherapy-related complications include the occurrence of hypothyroidism and cardiotoxicity. Metformin (MET) is a pharmacological agent for managing type 2 diabetes. It has been reported to mitigate certain toxic manifestations associated with chemotherapy. This study's primary objective is to investigate MET's protective effects against hypothyroidism and cardiotoxicity induced by CMF treatment. A total of forty male rats were allocated into four distinct groups, each consisting of ten rats per group. These groups were categorized as follows: saline, MET, CMF, and CMF + MET. The experimental group of rats were administered CMF via intraperitoneal injection, receiving two doses of CMF, and fed MET in their daily drinking water, with a 2.5 mg/mL concentration. Blood samples were collected into EDTA tubes for assessment of TSH, free and total (T4 and T3), troponin I, CK, and CK-MB levels utilizing Electrochemiluminescence Immunoassays (ECI). The saline and MET groups did not exhibit significant alterations in thyroid hormones or cardiotoxic biomarkers. In contrast, in the CMF group, there was a notable reduction in T4, FT4, T3, and FT3 levels but no significant changes in TSH levels; however, troponin I, CK, and CK-MB levels were notably elevated. MET co-treatment with CMF did not ameliorate these effects caused by CMF. In conclusion, CMF treatment induced hypothyroidism and cardiotoxicity in rats, but MET co-treatment did not rescue the reduction of thyroid hormones or the elevation of cardiotoxic biomarkers.

The relationship between dietary inflammatory index values and thyroid function in the US adult population: An analysis of the NHANES 2007-2012 cohort

OBJECTIVE

Researchers have developed the Dietary Inflammatory Index (DII) as a tool to quantify the inflammatory potential of a given diet. Higher DII scores indicated a more proinflammatory diet. While inflammation is known to have a strong impact on thyroid function, the precise nature of the association between DII scores and thyroid function has yet to be clarified. This study was conducted with the goal of exploring this relationship in a representative population of adults from the United States.

METHODS

For this study, we used data from the National Health and Nutrition Examination Survey (NHANES). Standardized questionnaires were used to collect demographic and dietary data from the participants, and laboratory tests were used to collect data on the participants' thyroid parameters and other relevant data. Linear regression models and smoothed curve fitting were used to assess the relationship between DII scores and thyroid function, with weighted data analyses and subgroup analyses being conducted as appropriate.

RESULTS

In total, 7712 subjects were recruited from the NHANES 2007-2012 cohort. Their weighted mean age was 44.87 (0.47) years, mean DII score was 1.41 (0.05). Mean FT3 was 3.20 (0.01) pg/mL and mean TT4 was 7.81 (0.03) µg/dL. In adjusted analyses, higher DII values were related to increases in FT3 (β = .007; p = .027) and TT4 (β = .050; p = .005) levels. Subgroup analyses showed a negative correlation between FT3 levels and DII scores in a population with high urinary iodine concentrations.

CONCLUSION

These data indicate that the consumption of a more proinflammatory diet, as evidenced by elevated DII scores, is correlated with significant increases in FT3 and TT4 levels. However, for people with high urinary iodine concentrations, a more proinflammatory diet was associated with lower FT3 levels. Additional research will be vital to clarify the mechanistic basis for these findings.

Higher Sensitivity to Thyroid Hormones May Be Linked to Maintaining the Healthy Metabolic Condition in People with Obesity: New Insight from NHANES

INTRODUCTION

Obesity contributes to the pathogenesis of diverse metabolic diseases, yet the mechanism underlying metabolically healthy obesity (MHO) remains elusive. Thyroid hormones and sensitivity to them have a major impact on metabolism. Our study aimed to investigate the association between MHO and thyroid hormone sensitivity.

METHODS

Thyroid hormone indices, including the thyroid-stimulating hormone (TSH) index (TSHI), the Thyrotroph Thyroxine Sensitivity Index (TTSI), the Thyroid Feedback Quantile-Based Index (TFQI), and the Parametric Thyroid Feedback Quantile-Based Index (PTFQI), were calculated based on a non-institutionalized US sample in the National Health and Nutrition Examination Survey (NHANES, 2007-2012). Participants were divided into four groups (metabolically healthy non-obesity [MHNO], metabolically unhealthy non-obesity [MUNO], MHO, and metabolically unhealthy obesity [MUO]) according to their body mass index and metabolic profiles. Linear regression, logistic regression, and restricted cubic splines were employed to analyze the association between thyroid hormone indices and metabolic phenotypes.

RESULTS

A total of 4,857 participants (49.6% men; mean age, 42.6 years) were included, with 1,539 having obesity and 235 identified as MHO. Participants in the MHO group exhibited lower levels of TSH, TSHI, TTSI, TFQI, and PTFQI compared with the MHNO group (all p < 0.05), while the differences among MHNO, MUNO, and MUO groups were not statistically significant (all p > 0.05). Among participants with obesity, TSH, TSHI, TTSI, TFQI, and PTFQI were positively associated with metabolic abnormality (all p < 0.05).

CONCLUSION

Participants with MHO exhibited higher thyroid hormone sensitivity among various obesity phenotypes, even when compared with those with MHNO. A positive association was observed between metabolic abnormality and thyroid hormone sensitivity, while the trend of TSH was observed to be consistent with sensitivity to thyroid hormone indices in discriminating metabolic abnormality. Hence, TSH has the potential to serve as a convenient index for detecting sensitivity to thyroid hormones and further metabolic conditions.

Endocrine disorders associated with obesity

Several endocrine disorders, including diabetes, insulinoma, Cushing syndrome, hypothyroidism, polycystic ovarian syndrome, and growth hormone deficiency, are associated with obesity. The mechanisms underlying the development of obesity vary according to the abnormalities of endocrine function. The primary actions of insulin, glucocorticoids (GCs), thyroid hormone, and growth hormone are associated with energy metabolism in the liver, muscle, adipose tissue, and other tissues. This chapter describes the pathogenesis of obesity and metabolic dysfunction associated with excess insulin or GCs and the deficiency of thyroid hormone or growth hormone.

Clinical and Biochemical Characteristics of Untreated Adult Patients With Resistance to Thyroid Hormone Alpha

Background

Thyroid hormone resistance due to pathogenic variants in thyroid hormone receptor alpha (THRA) is rare and descriptions of patients are sparse. The disorder is probably underdiagnosed as patients may have normal thyroid function tests. Treatment with thyroxine in childhood improves clinical symptoms. However, it is not clear if treatment has beneficial effects if started in adulthood.

Cases

We investigated 4 previously untreated Caucasian adult first-degree-related patients with the THRA c.788C > T, p.(Ala263Val) variant identified by a gene panel for intellectual disability in the index patient. Clinical data and previous investigations were obtained from medical reports.

Results

During childhood and adolescence, short stature, short limbs, metacarpals, and phalanges, and delayed bone age maturation were observed. Delayed motor and language development and decreased intellectual and learning abilities were described. Abdominal adiposity, round face, and increased head circumference were common features. All individuals complained of tiredness, constipation, and low mood. While thyrotropin (TSH) and free thyroxine (FT4) were within the reference range, free triiodothyronine (FT3) was high. FT4/FT3 ratio and reverse T3 were low. Other main features were low hemoglobin and high LDL/HDL ratio.

Conclusion

Investigation of 4 first-degree-related adult patients with untreated resistance to thyroid hormone alpha (RTHα) revealed more pronounced phenotype features and hypothyroid symptoms than previously described in patients treated with levothyroxine from childhood or adolescence. The delay in diagnosis is probably due to normal thyroid function tests. We suggest that THRA analysis should be performed in patients with specific clinical features, as treatment in early childhood may improve outcomes.

360-Degree Perspectives on Obesity

Alarming statistics show that the number of people affected by excessive weight has surpassed 2 billion, representing approximately 30% of the world's population. The aim of this review is to provide a comprehensive overview of one of the most serious public health problems, considering that obesity requires an integrative approach that takes into account its complex etiology, including genetic, environmental, and lifestyle factors. Only an understanding of the connections between the many contributors to obesity and the synergy between treatment interventions can ensure satisfactory outcomes in reducing obesity. Mechanisms such as oxidative stress, chronic inflammation, and dysbiosis play a crucial role in the pathogenesis of obesity and its associated complications. Compounding factors such as the deleterious effects of stress, the novel challenge posed by the obesogenic digital (food) environment, and the stigma associated with obesity should not be overlooked. Preclinical research in animal models has been instrumental in elucidating these mechanisms, and translation into clinical practice has provided promising therapeutic options, including epigenetic approaches, pharmacotherapy, and bariatric surgery. However, more studies are necessary to discover new compounds that target key metabolic pathways, innovative ways to deliver the drugs, the optimal combinations of lifestyle interventions with allopathic treatments, and, last but not least, emerging biological markers for effective monitoring. With each passing day, the obesity crisis tightens its grip, threatening not only individual lives but also burdening healthcare systems and societies at large. It is high time we took action as we confront the urgent imperative to address this escalating global health challenge head-on.

Effects of hormones on intestinal stem cells

The maintenance of intestinal renewal and repair mainly depends on intestinal stem cells (ISCs), which can also contribute to the growth of intestinal tumours. Hormones, which are vital signalling agents in the body, have various effects on the growth and replacement of intestinal stem cells. This review summarises recent progress in the identification of hormones associated with intestinal stem cells. Several hormones, including thyroid hormone, glucagon-like peptide-2, androgens, insulin, leptin, growth hormone, corticotropin-releasing hormone and progastrin, promote the development of intestinal stem cells. However, somatostatin and melatonin are two hormones that prevent the proliferation of intestinal stem cells. Therefore, new therapeutic targets for the diagnosis and treatment of intestinal illnesses can be identified by examining the impact of hormones on intestinal stem cells.

Hypothyroidism-associated immunosuppression involves induction of galectin-1-producing regulatory T cells

Hypothyroidism exerts deleterious effects on immunity, but the precise role of the hypothalamic-pituitary-thyroid (HPT) axis in immunoregulatory and tolerogenic programs is barely understood. Here, we investigated the mechanisms underlying hypothyroid-related immunosuppression by examining the regulatory role of components of the HPT axis. We first analyzed lymphocyte activity in mice overexpressing the TRH gene (Tg-Trh). T cells from Tg-Trh showed increased proliferation than wild-type (WT) euthyroid mice in response to polyclonal activation. The release of Th1 pro-inflammatory cytokines was also increased in Tg-Trh and TSH levels correlated with T-cell proliferation. To gain further mechanistic insights into hypothyroidism-related immunosuppression, we evaluated T-cell subpopulations in lymphoid tissues of hypothyroid and control mice. No differences were observed in CD3/CD19 or CD4/CD8 ratios between these strains. However, the frequency of regulatory T cells (Tregs) was significantly increased in hypothyroid mice, and not in Tg-Trh mice. Accordingly, in vitro Tregs differentiation was more pronounced in naïve T cells isolated from hypothyroid mice. Since Tregs overexpress galectin-1 (Gal-1) and mice lacking this lectin (Lgals1^-/- ) show reduced Treg function, we investigated the involvement of this immunoregulatory lectin in the control of Tregs in settings of hypothyroidism. Increased T lymphocyte reactivity and reduced frequency of Tregs were found in hypothyroid Lgals1^-/- mice when compared to hypothyroid WT animals. This effect was rescued by the addition of recombinant Gal-1. Finally, increased expression of Gal-1 was found in Tregs purified from hypothyroid WT mice compared with their euthyroid counterpart. Thus, a substantial increase in the frequency and activity of Gal-1-expressing Tregs underlies immunosuppression associated with hypothyroid conditions, with critical implications in immunopathology, metabolic disorders, and cancer.

GLIS3 regulates transcription of thyroid hormone biosynthetic genes in coordination with other thyroid transcription factors

BACKGROUND

Loss of the transcription factor GLI-Similar 3 (GLIS3) function causes congenital hypothyroidism (CH) in both humans and mice due to decreased expression of several thyroid hormone (TH) biosynthetic genes in thyroid follicular cells. Whether and to what extent, GLIS3 regulates thyroid gene transcription in coordination with other thyroid transcriptional factors (TFs), such as PAX8, NKX2.1 and FOXE1, is poorly understood.

METHODS

PAX8, NKX2.1, and FOXE1 ChIP-Seq analysis with mouse thyroid glands and rat thyrocyte PCCl3 cells was performed and compared to that of GLIS3 to analyze the co-regulation of gene transcription in thyroid follicular cells by these TFs.

RESULTS

Analysis of the PAX8, NKX2.1, and FOXE1 cistromes identified extensive overlaps between these TF binding loci and those of GLIS3 indicating that GLIS3 shares many of the same regulatory regions with PAX8, NKX2.1, and FOXE1, particularly in genes associated with TH biosynthesis, induced by thyroid stimulating hormone (TSH), and suppressed in Glis3KO thyroid glands, including Slc5a5 (Nis), Slc26a4, Cdh16, and Adm2. ChIP-QPCR analysis showed that loss of GLIS3 did not significantly affect PAX8 or NKX2.1 binding and did not cause major alterations in H3K4me3 and H3K27me3 epigenetic signals.

CONCLUSIONS

Our study indicates that GLIS3 regulates transcription of TH biosynthetic and TSH-inducible genes in thyroid follicular cells in coordination with PAX8, NKX2.1, and FOXE1 by binding within the same regulatory hub. GLIS3 does not cause major changes in chromatin structure at these common regulatory regions. GLIS3 may induce transcriptional activation by enhancing the interaction of these regulatory regions with other enhancers and/or RNA Polymerase II (Pol II) complexes.

Comprehensive Analysis of the Longissimus Dorsi Transcriptome and Metabolome Reveals the Regulatory Mechanism of Different Varieties of Meat Quality

The beef quality significantly varies between breeds. Pingliang Red Cattle resembles Wagyu in fat deposition and flavor. To screen key factors affecting beef quality, we performed meat quality trait testing, RNA-seq, and metabolomics on the longissimus dorsi of Pingliang Red Cattle, Wagyu cross F1 generation, and Simmental cattle. The gene and metabolite expression profiles were similar between Pingliang Red Cattle and Wagyu cross F1 generation. Genes such as FASN, ACACA, PLIN1, and FABP4 were significantly upregulated in the Pingliang Red Cattle and Wagyu cross F1 generation (P < 0.05). Similarly, numerous metabolites, such as 3-iodo-l-tyrosine, arachidonic acid, and cis-aconitate, which may improve the beef quality such as fat deposition and tenderness, were found in higher levels in the Pingliang Red Cattle and Wagyu cross F1 generation. This study revealed differences in the transcriptional and metabolic levels between Pingliang Red Cattle and premium beef breeds, suggesting that Pingliang Red Cattle harbors the genetic potential for breeding high-grade beef cattle.

A Comprehensive Review of Thyroid Hormone Metabolism in the Gut and Its Clinical Implications

Background: The gut is a target organ of thyroid hormone (TH) that exerts its action via the nuclear thyroid hormone receptor α1 (TRα1) expressed in intestinal epithelial cells. THs are partially metabolized via hepatic sulfation and glucuronidation, resulting in the production of conjugated iodothyronines. Gut microbiota play an important role in peripheral TH metabolism as they produce and secrete enzymes with deconjugation activity (β-glucuronidase and sulfatase), via which TH can re-enter the enterohepatic circulation. Summary: Intestinal epithelium homeostasis (the finely tuned balance between cell proliferation and differentiation) is controlled by the crosstalk between triiodothyronine and TRα1 and the presence of specific TH transporters and TH-activating and -inactivating enzymes. Patients and experimental murine models with a dominant-negative mutation in the TRα exhibit gross abnormalities in the morphology of the intestinal epithelium and suffer from severe symptoms of a dysfunctional gastrointestinal tract. Over the past decade, gut microbiota has been identified as an essential factor in health and disease, depending on its compositional and functional profile. This has led to a renewed interest in the so-called gut-thyroid axis. Disruption of gut microbial homeostasis (dysbiosis) is associated with autoimmune thyroid disease (AITD), including Hashimoto's thyroiditis, Graves' disease, and Graves' orbitopathy. These studies reviewed here provide new insights into the gut microbiota roles in thyroid disease pathogenesis and may be an initial step toward microbiota-based therapies in AITD. However, it should be noted that cause-effect mechanisms remain to be proven, for which prospective cohort studies, randomized clinical trials, and experimental studies are needed. Conclusion: This review aims at providing a comprehensive insight into the interplay between TH metabolism and gut homeostasis.

Assessment of the association between genetic factors regulating thyroid function and microvascular complications in diabetes: A two-sample Mendelian randomization study in the European population

BACKGROUND

Observational studies have identified a possible link between thyroid function and diabetic microangiopathy, specifically in diabetic kidney disease (DKD) and diabetic retinopathy (DR). However, it is unclear whether this association reflects a causal relationship.

OBJECTIVE

To assess the potential direct effect of thyroid characteristics on DKD and DR based on Mendelian randomization (MR).

METHODS

We conducted an MR study using genetic variants as an instrument associated with thyroid function to examine the causal effects on DKD and DR. The study included the analysis of 4 exposure factors associated with thyroid hormone regulation and 5 outcomes. Genomewide significant variants were used as instruments for standardized freethyroxine (FT4) and thyroid-stimulating hormone (TSH) levels within the reference range, standardized free triiodothyronine (FT3):FT4 ratio, and standardized thyroid peroxidase antibody (TPOAB) levels. The primary outcomes were DKD and DR events, and secondary outcomes were estimated glomerular filtration rate (eGFR), urinary albumin-to-creatinine ratio (ACR) in diabetes, and proliferative diabetic retinopathy (PDR). Satisfying the 3 MR core assumptions, the inverse-variance weighted technique was used as the primary analysis, and sensitivity analysis was performed using MR-Egger, weighted median, and MR pleiotropy residual sum and outlier techniques.

RESULTS

All outcome and exposure instruments were selected from publicly available GWAS data conducted in European populations. In inverse-variance weighted random-effects MR, gene-based TSH with in the reference range was associated with DKD (OR 1.44; 95%CI 1.04, 2.41; P = 0.033) and eGFR (β: -0.031; 95%CI: -0.063, -0.001; P = 0.047). Gene-based increased FT3:FT4 ratio, decreased FT4 with in the reference range were associated with increased ACR with inverse-variance weighted random-effects β of 0.178 (95%CI: 0.004, 0.353; P = 0.046) and -0.078 (95%CI: -0.142, -0.014; P = 0.017), respectively, and robust to tests of horizontal pleiotropy. However, all thyroid hormone instruments were not associated with DR and PDR at the genetic level.

CONCLUSION

In diabetic patients, an elevated TSH within the reference range was linked to a greater risk of DKD and decreased eGFR. Similarly, decreased FT4 and an increased FT3:FT4 ratio within the reference range were associated with increased ACR in diabetic patients. However, gene-based thyroid hormones were not associated with DR, indicating a possible pathway involving the thyroid-islet-renal axis. However, larger population studies are needed to further validate this conclusion.

Association Between Sensitivity to Thyroid Hormone Indices and Diabetic Retinopathy in Euthyroid Patients with Type 2 Diabetes Mellitus

OBJECTIVE

Normal thyroid hormone (TH) levels and their relation to microvascular complications in patients with type 2 diabetes mellitus (T2DM) have been studied. However, the relationship between TH sensitivity and diabetic retinopathy (DR) remains unclear. Thus, this study aimed to investigate the relationship between TH sensitivity and the risk of DR in euthyroid T2DM patients.

METHODS

This retrospective study analyzed 422 T2DM patients and calculated their sensitivity to TH indices. Multivariable logistic regression, generalized additive model, and subgroup analysis were performed to examine the association between sensitivity to TH indices and DR risk.

RESULTS

After adjusting for covariates, the binary logistic regression model showed no statistically significant association between the sensitivity of TH indices and the risk of DR in euthyroid T2DM patients. However, a non-linear relationship was found between sensitivity to TH indices (thyroid-stimulating hormone index, thyroid feedback quantile index [TFQI]) and the risk of DR in the crude model; TFQI and DR in the adjusted model. The inflection point of the TFQI was 0.23. The effect size (odds ratio) on the left and right of the inflection point were 3.19 (95% confidence interval [CI]: 1.24 to 8.17 p=0.02) and 0.11 (95% CI: 0.01, 0.93 p=0.04), respectively. Moreover, this relationship was maintained by men stratified by sex. In euthyroid patients with T2DM, an approximate inverted U-shaped relationship and a threshold effect were demonstrated between TH index sensitivity and DR risk with sex differences. This study provided an in-depth understanding of the relationship between thyroid function and DR, which has important clinical implications for risk stratification and individual prediction.

Role of Hormones During Gestation and Early Development: Pathways Involved in Developmental Programming

Accumulating evidence suggests that an altered maternal milieu and environmental insults during the intrauterine and perinatal periods of life affect the developing organism, leading to detrimental long-term outcomes and often to adult pathologies through programming effects. Hormones, together with growth factors, play critical roles in the regulation of maternal-fetal and maternal-neonate interfaces, and alterations in any of them may lead to programming effects on the developing organism. In this chapter, we will review the role of sex steroids, thyroid hormones, and insulin-like growth factors, as crucial factors involved in physiological processes during pregnancy and lactation, and their role in developmental programming effects during fetal and early neonatal life. Also, we will consider epidemiological evidence and data from animal models of altered maternal hormonal environments and focus on the role of different tissues in the establishment of maternal and fetus/infant interaction. Finally, we will identify unresolved questions and discuss potential future research directions.

Nuclear corepressor SMRT acts as a strong regulator of both β-oxidation and suppressor of fibrosis in the differentiation process of mouse skeletal muscle cells

BACKGROUND

Silencing Mediator of Retinoid and Thyroid hormone receptors (SMRT; NCoR2) is a transcriptional corepressor (CoR) which has been recognized as an important player in the regulation of hepatic lipogenesis and in somatic development in mouse embryo. SMRT protein is also widely expressed in mouse connective tissues, for example adipocytes and muscle. We recently reported that mice with global deletion of SMRT develop significant obesity and muscle wasting which are independent from thyroid hormone (TH) signaling and thermogenesis. However, the tissue specific role of SMRT in skeletal muscle is still not clear.

METHODS

To clarify role of SMRT in muscle differentiation, we made myogenic C2C12 clones which lack SMRT protein (C2C12-SKO) by using CRISPR-Cas9. Wild-type C2C12 (C2C12-WT) and C2C12-SKO cells were cultured in differentiation medium, and the resulting gene and protein profiles were compared between the two cell lines both before and after differentiation. We also analyzed muscle tissues which were dissected from whole body SMRT knockout (KO) mice and their controls.

RESULTS

We found significant up-regulation of muscle specific β-oxidation markers; Peroxisome proliferator-activated receptor δ (PPARδ) and PPARγ coactivator-1α (PGC-1α) in the C2C12-SKO cells, suggesting that the cells had a similar gene profile to what is found in exercised rodent skeletal muscle. On the other hand, confocal microscopic analysis showed the significant loss of myotubes in C2C12-SKO cells similar to the morphology found in immature myoblasts. Proteomics analysis also confirmed that the C2C12-SKO cells had higher expression of markers of fibrosis (ex. Collagen1A1; COL1A1 and Fibroblast growth factor-2; FGF-2), indicating the up-regulation of Transforming growth factor-β (TGF-β) receptor signaling. Consistent with this, treatment with a specific TGF-β receptor inhibitor ameliorated both the defects in myotube differentiation and fibrosis.

CONCLUSION

Taken together, we demonstrate that SMRT functions as a pivotal transcriptional mediator for both β-oxidation and the prevention for the fibrosis via TGF-β receptor signaling in the differentiation of C2C12 myoblasts. In contrast to the results from C2C12 cells, SMRT does not appear to play a role in adult skeletal muscle of whole body SMRT KO mice. Thus, SMRT plays a significant role in the differentiation of myoblasts.

What we know about the relationship between autoimmune thyroid diseases and gut microbiota: a perspective on the role of probiotics on pediatric endocrinology

INTRODUCTION

Autoimmune diseases account for a cumulative overall prevalence of about 3-5% worldwide. Among them, autoimmune thyroid diseases (ATDs) are the most common and comprise two main entities: Hashimoto's thyroiditis (HT) and Graves-Basedow disease (GD). The pathogenesis of ATDs remains not fully elucidated, however the role of microbioma has been proposed. Gut microbiota exert an important influence on the intestinal barrier, nutrient metabolism and immune system development and functions.

EVIDENCE ACQUISITION

In this review, we describe on the main features of ATDs in pediatrics, focusing on the reciprocal influence between gut microbiota, thyroid hormone metabolism and thyroid autoimmunity and consider the role of probiotics and other microbiota-targeted therapies in thyroid diseases with a perspective on pediatric endocrinology.

EVIDENCE SYNTHESIS

Microbiome affects both endogenous and exogenous thyroid hormone metabolism and influences the absorption of minerals important to the thyroid function, which are iodine, selenium, zinc and iron. The alteration of the gut microbiota, with the consequent modifications in the barrier function and the increased gut permeability, seems involved in the development of autoimmune and chronic inflammatory diseases, including ATDs. The supplementation with probiotics showed beneficial effects on the thyroid hormone and thyroid function because this strategy could restore the intestinal eubiosis and the good strain microorganism proliferation.

CONCLUSIONS

Even though the evidence about the interaction between microbiota and ATDs in pediatric patients is limited, the promising results obtained in the adult population, and in other autoimmune disorders affecting children, highlight the need of for further research in the pediatric field.

Thyroid hormone regulators in human cerebral cortex development

Brain development is critically dependent on the timely supply of thyroid hormones. The thyroid hormone transporters are central to the action of thyroid hormones in the brain, facilitating their passage through the blood-brain barrier. Mutations of the monocarboxylate transporter 8 (MCT8) cause the Allan-Herndon-Dudley syndrome, with altered thyroid hormone concentrations in the blood and profound neurological impairment and intellectual deficit. Mouse disease models have revealed interplay between transport, deiodination, and availability of T3 to receptors in specific cells. However, the mouse models are not satisfactory, given the fundamental differences between the mouse and human brains. The goal of the present work is to review human neocortex development in the context of thyroid pathophysiology. Recent developments in single-cell transcriptomic approaches aimed at the human brain make it possible to profile the expression of thyroid hormone regulators in single-cell RNA-Seq datasets of the developing human neocortex. The data provide novel insights into the specific cellular expression of thyroid hormone transporters, deiodinases, and receptors.

Retrospective analysis and literature review of four cases of thyroid hormone resistance syndrome caused by THRB gene mutation

BACKGROUND

To summarize the clinical characteristics, genetics and follow-up data of four children with thyroid hormone resistance (RTH) syndrome and review the related literatures.

METHODS

The clinical data of the four children diagnosed with RTH syndrome in our hospital from 2018 to 2020 were retrospectively analyzed. Next-generation sequencing of the candidate genes related to thyroid diseases was performed using the blood collected from all the children and their parents who signed an informed consent. Then, relevant cases were retrieved on medical literature databases for analysis and summary.

RESULTS

Among the four cases, three cases of goiter; two cases of tachycardia, palpitations, personality change, hyperactivity, weight loss; one case of academic performance decline, and no hearing and vision loss were observed. Laboratory thyroid function tests indicated a mild increase in free triiodothyronine and with or without increased free thyroxine levels. Thyroid-stimulating hormone (TSH) levels were normal or slightly elevated, but thyrotropin receptor autoantibodies were negative. Octreotide inhibition test showed that the TSH levels of all the children decreased by more than 50% compared with the basal value (the genes of four cases were positive). However, magnetic resonance imaging of the pituitary gland showed no abnormalities. Related gene detection in the children and their families showed that four cases had THRB mutations: two proband mutations were from their fathers, and two cases had de novo mutations.

CONCLUSIONS

The clinical manifestations of pediatric RTH syndrome vary, and the diagnosis mainly depends on thyroid function tests. Heterozygous mutations in THRB are overall rare, even if with the advanced development of next-generation sequencing, not all the children with RTH syndrome have mutations. Furthermore, octreotide inhibition tests cannot be used as a diagnostic criterion to distinguish RTH syndrome from pituitary tumors in children.

Oxidative stress in Hashimoto's thyroiditis: possible adjuvant therapies to attenuate deleterious effects

A number of studies have shown that oxidative stress is related to the pathogenesis of several immunological diseases, such as Hashimoto's thyroiditis (HT), although there is no plausible mechanism to explain it. Thus, we aimed at hypothesizing and providing some possible mechanisms linking oxidative stress to autoimmunity aspects and its implications for HT, as well as adjuvant therapeutic proposals to mitigate the deleterious effects. Our hypothesis is that deficient eating habits, autoimmune regulator gene predisposing gene, dysbiosis and molecular mimicry, unfolded proteins and stress in the endoplasmic reticulum, and thymus involution appear to be the main potential factors leading to HT oxidative stress. Likewise, we show that the use of minerals selenium and zinc, vitamins D and C, as well as probiotics, can be interesting adjuvant therapies for the control of oxidative damage and poor prognosis of HT. Further clinical trials are needed to understand the real beneficial and side effects of these supplements.

Azole-Induced Color Vision Deficiency Associated with Thyroid Hormone Signaling: An Integrated In Vivo, In Vitro, and In Silico Study

Azoles that are used in pesticides, pharmaceuticals, and personal care products can have toxic effects on fish. However, there is no information regarding azole-induced visual disorder associated with thyroid disruption. We evaluated changes in retinal morphology, optokinetic response, transcript abundance of the genes involved in color perception and hypothalamic-pituitary-thyroid (HPT) axis, and thyroid hormone (TH) levels in zebrafish larvae exposed to common azoles, such as climbazole (CBZ, 0.1 and 10 μg/L) and triadimefon (TDF, 50 and 500 μg/L), at environmentally relevant and predicted worst-case environmental concentrations. Subsequently, the effect of azoles on TH-dependent GH3 cell proliferation and thyroid receptor (TR)-regulated transcriptional activity, as well as the in silico binding affinity between azoles and TR isoforms, was investigated. Azole exposure decreased cell densities of the ganglion cell layer, inner nuclear layer, and photoreceptor layer. Zebrafish larvae exposed to environmentally relevant concentrations of CBZ and TDF showed a decrease in optokinetic response to green-white and red-white stripes but not blue-white stripes, consistent with disturbance in the corresponding opsin gene expression. Azole exposure also reduced triiodothyronine levels and concomitantly increased HPT-related gene expression. Molecular docking analysis combined with in vitro TR-mediated transactivation and dual-luciferase reporter assays demonstrated that CBZ and TDF exhibited TR antagonism. These results are comparable to those obtained from a known TR antagonist, namely, TR antagonist 1, as a positive control. Therefore, damage to specific color perception by azoles appears to result from lowered TH signaling, indicating the potential threat of environmental TH disruptors to the visual function of fish.

Thyroid hormone-dependent oligodendroglial cell lineage genomic and non-genomic signaling through integrin receptors

Multiple sclerosis (MS) is a heterogeneous autoimmune disease whereby the pathological sequelae evolve from oligodendrocytes (OLs) within the central nervous system and are targeted by the immune system, which causes widespread white matter pathology and results in neuronal dysfunction and neurological impairment. The progression of this disease is facilitated by a failure in remyelination following chronic demyelination. One mediator of remyelination is thyroid hormone (TH), whose reliance on monocarboxylate transporter 8 (MCT8) was recently defined. MCT8 facilitates the entry of THs into oligodendrocyte progenitor cell (OPC) and pre-myelinating oligodendrocytes (pre-OLs). Patients with MS may exhibit downregulated MCT8 near inflammatory lesions, which emphasizes an inhibition of TH signaling and subsequent downstream targeted pathways such as phosphoinositide 3-kinase (PI3K)-Akt. However, the role of the closely related mammalian target of rapamycin (mTOR) in pre-OLs during neuroinflammation may also be central to the remyelination process and is governed by various growth promoting signals. Recent research indicates that this may be reliant on TH-dependent signaling through β1-integrins. This review identifies genomic and non-genomic signaling that is regulated through mTOR in TH-responsive pre-OLs and mature OLs in mouse models of MS. This review critiques data that implicates non-genomic Akt and mTOR signaling in response to TH-dependent integrin receptor activation in pre-OLs. We have also examined whether this can drive remyelination in the context of neuroinflammation and associated sequelae. Importantly, we outline how novel therapeutic small molecules are being designed to target integrin receptors on oligodendroglial lineage cells and whether these are viable therapeutic options for future use in clinical trials for MS.

Thyroid Diseases and Thyroid Asymptomatic Dysfunction in People Living With HIV

Thyroid diseases (TDs) and thyroid asymptomatic dysfunctions (TADs) are correlated with Human Immunodeficiency virus (HIV) infection and Acquired ImmunoDeficiency Syndrome (AIDS) as well as many endocrine dysfunctions and dysregulation of hormonal axes. To date, available studies on People Living With HIV (PLWH) affected by thyroid diseases and asymptomatic dysfunctions are few and rather controversial. The purpose of the present non-systematic literature review is to recap the current knowledge on the main features of thyroid dysfunctions and disorders in PLWH. Large cohort studies are needed for a better comprehension of the impact, evolution and treatment of thyroid pathologies in the HIV-infected population.

The relationship between TSH levels and clinical pregnancy outcomes for patients who undergo in vitro fertilization/intracytoplasmic sperm injection: a retrospective study

BACKGROUND

Thyroid dysfunction is linked with adverse pregnancy outcomes, an upper limit of a normal thyroid-stimulating hormone (TSH) threshold of 4.12-4.5 mIU/L should be considered for subclinical hypothyroidism in the infertile female population. Whereas, it's controversial whether or not the infertility thresholds for upper limit of TSH threshold of 2.5 mIU/L. In our study examines the correlation of optimal TSH levels and clinical pregnancy outcomes after fresh in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) embryo transfer cycles.

METHODS

Patients who underwent fresh IVF/ICSI embryo transfer cycles for the first time who presented between January 1, 2015 and December 31, 2017 at the Chongqing Institute of Reproductive and Genetic, Chongqing Health Center for Women and Children were enrolled. We excluded patients with ≥40 years, body mass index (BMI) ≤18 or ≥28 kg/m², the man with severe oligoasthenospermia, women with poor ovarian reserve, and presence of endocrine disorders, uterine anomaly, sactosalpinx, abnormal thyroid function, preimplantation genetic diagnosis, and chromosomal abnormality or polymorphism. Baseline characteristics and clinical pregnancy outcomes were observed in our study. We detected between TSH levels and clinical pregnancy outcomes in patients undergoing IVF/ICSI by Receiver operating characteristic (ROC) curves and logical regression.

RESULTS

A total of 6,088 patients who undergo IVF/ICSI were included. We first detected that the live birth rate had a statistically significant difference when the TSH level was 3 mIU/L. With the TSH ≤3 mIU/L group having a higher live birth rate than the TSH >3 mIU/L group (51.79% vs. 47.89%, P=0.024), meanwhile no significant difference were revealed between the early miscarriage rate (12.54% vs. 14.97%, P=0.091) and early clinical pregnancy rate (59.21% vs. 56.32%, P=0.114). There were no differences in pregnancy outcomes when the TSH threshold was at 3.5 or 4 mIU/L and no association was detected between TSH levels and clinical pregnancy outcomes in patients undergoing IVF/ICSI by ROC curves and logical regression.

CONCLUSIONS

Patients undergoing IVF/ICSI with a serum TSH level ≤3 mIU/L may have a higher live birth rate rather than ≤2.5 or ≤4 mIU/L.

Influence of Altered Thyroid Hormone Mechanisms in the Progression of Metabolic Dysfunction Associated with Fatty Liver Disease (MAFLD): A Systematic Review

We performed a systematic review of the mechanisms of thyroid hormones (THs) associated with metabolic dysfunction associated with fatty liver disease (MAFLD). This systematic review was registered under PROSPERO (CRD42022323766). We searched the MEDLINE (via PubMed) and Embase databases from their inception to March 2022. We included studies that assessed thyroid function by measuring the serum level of THs and those involved in MAFLD. We excluded reviews, case reports, editorials, letters, duplicate studies and designed controls. Forty-three studies included MAFLD, eleven analyzed THs, and thirty-two evaluated the mechanisms of THs in MAFLD. Thyroid hormones are essential for healthy growth, development and tissue maintenance. In the liver, THs directly influence the regulation of lipid and carbohydrate metabolism, restoring the homeostatic state of the body. The selected studies showed an association of reduced levels of THs with the development and progression of MAFLD. In parallel, reduced levels of T3 have a negative impact on the activation of co-regulators in the liver, reducing the transcription of genes important in hepatic metabolism. Overall, this is the first review that systematically synthesizes studies focused on the mechanism of THs in the development and progression of MAFLD. The data generated in this systematic review strengthen knowledge of the impact of TH changes on the liver and direct new studies focusing on therapies that use these mechanisms.

TRα2—An Untuned Second Fiddle or Fine-Tuning Thyroid Hormone Action?

Thyroid hormones (THs) control a wide range of physiological functions essential for metabolism, growth, and differentiation. On a molecular level, TH action is exerted by nuclear receptors (TRs), which function as ligand-dependent transcription factors. Among several TR isoforms, the function of TRα2 remains poorly understood as it is a splice variant of TRα with an altered C-terminus that is unable to bind T3. This review highlights the molecular characteristics of TRα2, proposed mechanisms that regulate alternative splicing and indications pointing towards an antagonistic function of this TR isoform in vitro and in vivo. Moreover, remaining knowledge gaps and major challenges that complicate TRα2 characterization, as well as future strategies to fully uncover its physiological relevance, are discussed.

Characterization of Thyroid Hormones Antivertigo Effects in a Rat Model of Excitotoxically-Induced Vestibulopathy

Impaired vestibular function induces disabling symptoms such as postural imbalance, impaired locomotion, vestibulo-ocular reflex alteration, impaired cognitive functions such as spatial disorientation, and vegetative deficits. These symptoms show up in sudden attacks in patients with Ménière or neuritis and may lead to emergency hospitalizations. To date, however, there is no curative solution to these pathologies and the effectiveness of treatments used to reduce symptoms in the management of patients is discussed. Thus, elucidating the biological mechanisms correlated to the expression kinetics of the vestibular syndrome is useful for the development of potential therapeutic candidates with a view to relieving patients and limiting emergency hospitalizations. Recently, a robust antivertigo effect of thyroxine (T4) was demonstrated in a rodent model of impaired vestibular function induced by unilateral surgical section of the vestibular nerve. The aim of the present study was to assess thyroid hormones L-T4 and triiodothyronine (T3) as well as the bioactive thyroid hormone metabolite TRIAC on a rodent model of acute unilateral vestibulopathy more representative of clinical vestibular pathology. To this end, a partial and transient unilateral suppression of peripheral vestibular inputs was induced by an excitotoxic lesion caused by transtympanic injection of kainic acid (TTK) into the inner ear of adult rats. Vestibular syndrome and functional recovery were studied by semi-quantitative and quantitative assessments of relevant posturo-locomotor parameters. In contrast to the effect previously demonstrated in the complete and irreversible vestibular injury model, administration of thyroxine in the TTK rodent model did not display significant antivertigo effect. However, it is noteworthy that administration of thyroxine showed trends to prevent posturo-locomotor alterations. Furthermore, the results of the current study suggested that a single dose of thyroxine is sufficient to induce the same effects on vestibular syndrome observed with sub-chronic administration, and that reducing the T4 dose may more efficiently prevent the appearance of vestibular deficits induced by the excitotoxic type lesion. Finally, comparison of the antivertigo effect of T4 in different vestibulopathy models enables us to determine the therapeutic indication in which thyroxine could be a potential therapeutic candidate.

Iodine deficiency is associated with increased thyroid hormone sensitivity in individuals with elevated TSH

Objective

Central sensitivity of thyroid hormone refers to the sensitivity of hypothalamic-pituitary-thyroid (HPT) axis to the change in circulating free thyroxine (fT4). A complex relationship exists between thyroxine levels and iodine nutritional status. To explore the relationship between thyroid hormone sensitivity and iodine nutritional status in elevated thyrotropin (TSH), we used national data to assess the relationship between thyroid hormone sensitivity and iodine nutritional status with contrasting demographic characteristics in China.

Methods

We enrolled 12,197 participants with TSH > 4.2 mIU/L from China. Serum and urine samples were collected, and we measured serum fT4, TSH, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) levels and urinary iodine concentration (UIC). The thyroid hormone sensitivity indices were calculated based on fT4 and TSH. The thyroid feedback quantile-based index (TFQI) is a new index to reflect thyroid hormone sensitivity. Higher TFQI quartiles indicated lower thyroid hormone sensitivity.

Results

The odds ratios (ORs) for the fourth versus first TFQI quartile were 0.84 (95% CI 0.72-0.99) for iodine deficiency, 1.24 (95% CI 1.05-1.47) for TPOAb+, and 0.44 (95% CI 0.40-0.50) for females. The OR of the fourth and first TFQI quartiles for age <30 years and >60 years was 2.09 (95% CI 1.82-2.41) and 1.19 (95% CI 1.05-1.36), respectively (P < 0.05). Other thyroid sensitivity indices also yielded similar results.

Conclusion

Thyroid hormone sensitivity and age have a U-shaped association in individuals with elevated TSH. Increased thyroid hormone sensitivity is associated with iodine deficiency and the female gender. Decreased thyroid hormone sensitivity is associated with TPOAb+. These findings are interesting and potentially useful for understanding the interaction between iodine nutrition and the hypothalamic-pituitary-thyroid axis.

Consumption of water contaminated by nitrate and its deleterious effects on the human thyroid gland: a review and update

Nowadays, the nitrates have been established as carcinogenic components due to the endogenous formation of N-nitroso compounds, however, the consumption of water contaminated with nitrates has only been strongly related to the presence of methemoglobinemia in infants, as an acute effect, leaving out other side effects that demand attention. The thyroid gland takes relevance because it can be altered by many pollutants known as endocrine disruptors, which are agents capable of interfering with the synthesis of hormones, thus far, it is known that nitrates may disrupt the amount of iodine uptake causing most of the time hypothyroidism and affecting the metabolic functions of the organism in all development stages, resulting in an important health burden for the exposed population. Here, this review and update highlighted the impact of consumption of water contaminated with nitrates and effects on the thyroid gland in humans, concluding that nitrates could act as true endocrine disruptor.

What is the Role of Thyroid Hormone Receptor Alpha 2 (TRα2) in Human Physiology?

Thyroid hormone receptors are nuclear receptors that function as transcription factors and are regulated by thyroid hormones. To date, a number of variants and isoforms are known. This review focuses on the thyroid hormone receptor α (TRα), in particular TRα2, an isoform that arises from alternative splicing of the THRA mRNA transcript. Unlike the TRα1 isoform, which can bind T3, the TRα2 isoform lacks a ligand-binding domain but still binds to DNA thereby antagonizing the transcriptional activity of TRα1. Although a regulatory role has been proposed, the physiological function of this TRα2 antagonism is still unclear due to limited in vitro and mouse model data. Recently, the first patients with resistance to thyroid hormone due to mutations in THRA, the TRα encoding gene, affecting the antagonistic function of TRα2 were described, suggesting a significant role of this particular isoform in human physiology.