Melissa officinalis extract palliates redox imbalance and inflammation associated with hyperthyroidism-induced liver damage by regulating Nrf-2/ Keap-1 gene expression in γ-irradiated rats.

BACKGROUND: Melissa officinalis (MO) is a well-known medicinal plant species used in the treatment of several diseases; it is widely used as a vegetable, adding flavour to dishes. This study was designed to evaluate the therapeutic effect of MO Extract against hyperthyroidism induced by Eltroxin and γ-radiation. METHODS: Hyperthyroidism was induced by injecting rats with Eltroxin (100 µg/kg/ day) for 14 days and exposure to γ-radiation (IR) (5 Gy single dose). The hyperthyroid rats were orally treated with MO extract (75 mg/kg/day) at the beginning of the second week of the Eltroxin injection and continued for another week. The levels of thyroid hormones, liver enzymes and proteins besides the impaired hepatic redox status and antioxidant parameters were measured using commercial kits. The hepatic gene expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its inhibitor Kelch-like ECH-associated protein-1(Keap-1) in addition to hepatic inflammatory mediators including tumor necrosis factor-α (TNF- α), Monocyte chemoattractant protein-1 (MCP-1) and fibrogenic markers such as transforming growth factor-beta1 (TGF-ß1) were determined. RESULTS: MO Extract reversed the effect of Eltroxin + IR on rats and attenuated the thyroid hormones. Moreover, it alleviated hyperthyroidism-induced hepatic damage by inhibiting the hepatic enzymes' activities as well as enhancing the production of proteins concomitant with improving cellular redox homeostasis by attenuating the deranged redox balance and modulating the Nrf2/Keap-1 pathway. Additionally, MO Extract alleviated the inflammatory response by suppressing the TNF- α and MCP-1 and prevented hepatic fibrosis via Nrf2-mediated inhibition of the TGF-ß1/Smad pathway. CONCLUSION: Accordingly, these results might strengthen the hepatoprotective effect of MO Extract in a rat model of hyperthyroidism by regulating the Nrf-2/ Keap-1 pathway.

Twin study: genotype-dependent epigenetic factors affecting free thyroxine levels in the normal range.

Aim: To explore the clinical application of DNA methylation affecting thyroid function, we evaluated the association of DNA methylation with free thyroxine (FT4) and TSH measurements in monozygotic twins. Materials & methods: Discordant pairs for FT4 or TSH levels were examined for the relationship between the within-pair difference of each measurement and the DNA methylation levels using epigenome-wide association studies. The contribution of polymorphisms to the methylation sensitivity was also examined. Results: We found two CpG sites significantly associated with FT4 levels, and also some CpG sites showing significant differences in their methylation levels within FT4-discordant pairs depending on the polymorphism in EPHB2. Conclusion: The FT4 level may be associated with a combination of methylation and polymorphisms in the EPHB2 gene.

Association of DIO2 and MCT10 Polymorphisms With Persistent Symptoms in LT4-Treated Patients in the UK Biobank.

CONTEXT: Some evidence suggests gene-treatment interactions might cause persistent symptoms in individuals receiving levothyroxine (LT4) treatment. OBJECTIVE: We investigated, as previously hypothesized, if single-nucleotide variations (SNVs; formerly single-nucleotide polymorphisms) in rs225014 (Thr92Ala), rs225015, or rs12885300 (ORFa-Gly3Asp) in the deiodinase 2 gene (DIO2), or rs17606253 in the monocarboxylate transporter 10 gene (MCT10) were associated with outcomes indicative of local tissue hypothyroidism in LT4-treated patients and controls. METHODS: We included 18 761 LT4-treated patients and 360 534 controls in a population-based cross-sectional study in the UK Biobank. LT4 treatment was defined as a diagnosis of hypothyroidism and self-reported use of LT4 without use of 3,5,3'-triiodothyronine. Outcomes were psychological well-being, cognitive function, and cardiovascular risk factors. Associations were evaluated by linear, logistic, or ordinal logistic multiple regression. Adjustments included sex, age, sex-age interaction, and genetic principal components 1 to 10. RESULTS: Compared to controls, LT4 treatment was adversely associated with almost all outcomes, most noteworthy: Increased frequency of tiredness (P < .001), decreased well-being factor score (P < .001), increased reaction-time (P < .001), and increased body mass index (P < .001). Except for a significant association between the minor rs225015 A allele and financial dissatisfaction, there was no association of rs225014, rs225015, rs12885300, or rs17606253 with any outcomes in LT4-treated patients. For all outcomes, carrying the risk allele at these 4 SNVs did not amplify symptoms associated with LT4 treatment compared to controls. CONCLUSION: rs225014, rs225015, rs12885300, and rs17606253 could not explain changed psychological well-being, cognitive function, or cardiovascular risk factors in LT4-treated patients. Our findings do not support a gene-treatment interaction between these SNVs and LT4 treatment.

Effects of genetic selection for fast growth on the development of wooden breast myopathy in broilers.

1. This study investigated the physiological and molecular mechanisms leading to wooden breast (WB) by comparing growth parameters, oxygen consumption rate, thyroid hormone and gene expression patterns in fast- versus slow-growing broiler lines (Cobb500 and L1986, respectively).2. WB was observed in Cobb500 broilers only and was first diagnosed on d 21 post-hatch. Compared to the slow-growing L1986, Cobb500 showed a significantly higher growth rate, relative breast weight, breast thickness, meat pH and water-retention capacity (drip loss). Correspondingly, there was significantly lower relative heart weight, relative right ventricular weight, triiodothyronine and thyroxine concentrations and oxygen consumption rate.3. Compared to No-WB Cobb500, the WB-affected samples exhibited higher relative breast weight, breast thickness and drip loss and lower plasma total thyroxine (T4) concentrations.4. Selection for fast growth was associated with differential expression of genes involved in hypoxia (PLOD2), energy metabolism (FABP3, FABP4, CD36, and LPL), endoplasmic reticulum stress, muscle regeneration (CSRP3) and fibre-type switching (ANKRD1). WB-affected samples exhibited an upregulation of CSRP3, PLOD2 and ANKRD1, while CD36 was downregulated. Taken together, selection for fast growth and muscle gain is not matched by adequate cardiac and metabolic support systems.

Investigation of common genetic risk factors between thyroid traits and breast cancer.

Breast cancer (BC) risk is suspected to be linked to thyroid disorders, however observational studies exploring the association between BC and thyroid disorders gave conflicting results. We proposed an alternative approach by investigating the shared genetic risk factors between BC and several thyroid traits. We report a positive genetic correlation between BC and thyroxine (FT4) levels (corr = 0.13, p-value = 2.0 × 10-4) and a negative genetic correlation between BC and thyroid-stimulating hormone (TSH) levels (corr = -0.09, p-value = 0.03). These associations are more striking when restricting the analysis to estrogen receptor-positive BC. Moreover, the polygenic risk scores (PRS) for FT4 and hyperthyroidism are positively associated to BC risk (OR = 1.07, 95%CI: 1.00-1.13, p-value = 2.8 × 10-2 and OR = 1.04, 95%CI: 1.00-1.08, p-value = 3.8 × 10-2, respectively), while the PRS for TSH is inversely associated to BC risk (OR = 0.93, 95%CI: 0.89-0.97, p-value = 2.0 × 10-3). Using the PLACO method, we detected 49 loci associated to both BC and thyroid traits (p-value < 5 × 10-8), in the vicinity of 130 genes. An additional colocalization and gene-set enrichment analyses showed a convincing causal role for a known pleiotropic locus at 2q35 and revealed an additional one at 8q22.1 associated to both BC and thyroid cancer. We also found two new pleiotropic loci at 14q32.33 and 17q21.31 that were associated to both TSH levels and BC risk. Enrichment analyses and evidence of regulatory signals also highlighted brain tissues and immune system as candidates for obtaining associations between BC and TSH levels. Overall, our study sheds light on the complex interplay between BC and thyroid traits and provides evidence of shared genetic risk between those conditions.

[Genetic mutation profiles for children with congenital hypothyroidism in Fujian province].

Objective: To explore the mutation characteristics of pathogenic genes in children with congenital hypothyroidism (CH) in Fujian. Methods: The clinical data of 116 unrelated CH children diagnosed in Fujian Provincial Maternal and Child Health Hospital from January 2019 to September 2020 were retrospectively analyzed, including 50 females and 66 males, with an average age of (20±10) days at diagnosis. Targeted exome sequencing technology was used to detect the mutation frequency, type and distribution characteristics of 29 genes related to thyroxine synthesis or thyroid development. Results: Three hundred and fifty-one potential functional mutations were detected in 105 of 116 CH patients, with a detection rate of 90.5% (105/116). DUOX2 (66.4%, 77/116) was the most frequent mutated gene, followed by TG (23.3%, 27/116), DUOXA1 (23.3%, 27/116), and TPO (12.1%, 14/116), which were all involved in thyroid hormone synthesis. Among the 105 children with CH, 70 cases carried double allele mutation. Except for 3 cases of thyroid dysplasia related genes (2 cases of TSHR and 1 case of GLIS3), the rest were also related to thyroid hormone synthesis. The gene with the highest carrier rate was DUOX2 (68.8%, 59/70), followed by TG (8.6%, 6/70), TPO (4.3%, 3/70), DUOXA2 (1.4%, 1/70) and DUOXA1 (1.4%, 1/70). Conclusion: The main mutated genes in CH children in Fujian are the key genes involved in thyroid hormone synthesis, such as DUOX2, TG and TPO.

Epigenome-Wide Association Study Reveals CpG Sites Associated with Thyroid Function and Regulatory Effects on KLF9.

Background: Thyroid hormones play a key role in differentiation and metabolism and are known regulators of gene expression through both genomic and epigenetic processes including DNA methylation. The aim of this study was to examine associations between thyroid hormones and DNA methylation. Methods: We carried out a fixed-effect meta-analysis of epigenome-wide association study (EWAS) of blood DNA methylation sites from 8 cohorts from the ThyroidOmics Consortium, incorporating up to 7073 participants of both European and African ancestry, implementing a discovery and replication stage. Statistical analyses were conducted using normalized beta CpG values as dependent and log-transformed thyrotropin (TSH), free thyroxine, and free triiodothyronine levels, respectively, as independent variable in a linear model. The replicated findings were correlated with gene expression levels in whole blood and tested for causal influence of TSH and free thyroxine by two-sample Mendelian randomization (MR). Results: Epigenome-wide significant associations (p-value <1.1E-7) of three CpGs for free thyroxine, five for free triiodothyronine, and two for TSH concentrations were discovered and replicated (combined p-values = 1.5E-9 to 4.3E-28). The associations included CpG sites annotated to KLF9 (cg00049440) and DOT1L (cg04173586) that overlap with all three traits, consistent with hypothalamic-pituitary-thyroid axis physiology. Significant associations were also found for CpGs in FKBP5 for free thyroxine, and at CSNK1D/LINCO1970 and LRRC8D for free triiodothyronine. MR analyses supported a causal effect of thyroid status on DNA methylation of KLF9. DNA methylation of cg00049440 in KLF9 was inversely correlated with KLF9 gene expression in blood. The CpG at CSNK1D/LINC01970 overlapped with thyroid hormone receptor alpha binding peaks in liver cells. The total additive heritability of the methylation levels of the six significant CpG sites was between 25% and 57%. Significant methylation QTLs were identified for CpGs at KLF9, FKBP5, LRRC8D, and CSNK1D/LINC01970. Conclusions: We report novel associations between TSH, thyroid hormones, and blood-based DNA methylation. This study advances our understanding of thyroid hormone action particularly related to KLF9 and serves as a proof-of-concept that integrations of EWAS with other -omics data can provide a valuable tool for unraveling thyroid hormone signaling in humans by complementing and feeding classical in vitro and animal studies.

The Developmental Progression of Eight Opsin Spectral Signals Recorded from the Zebrafish Retinal Cone Layer Is Altered by the Timing and Cell Type Expression of Thyroxin Receptor ß2 (trß2) Gain-Of-Function Transgenes.

Zebrafish retinal cone signals shift in spectral shape through larval, juvenile, and adult development as expression patterns of eight cone-opsin genes change. An algorithm extracting signal amplitudes for the component cone spectral types is developed and tested on two thyroxin receptor ß2 (trß2) gain-of-function lines crx:mYFP-2A-trß2 and gnat2:mYFP-2A-trß2, allowing correlation between opsin signaling and opsin immunoreactivity in lines with different developmental timing and cell-type expression of this red-opsin-promoting transgene. Both adult transgenics became complete, or nearly complete, "red-cone dichromats," with disproportionately large long-wavelength-sensitive (LWS)1 opsin amplitudes as compared with controls, where LWS1 and LWS2 amplitudes were about equal, and significant signals from SWS1, SWS2, and Rh2 opsins were detected. But in transgenic larvae and juveniles of both lines it was LWS2 amplitudes that increased, with LWS1 cone signals rarely encountered. In gnat2:mYFP-2A-trß2 embryos at 5 d postfertilization (dpf), red-opsin immunoreactive cone density doubled, but red-opsin amplitudes (LWS2) increased <10%, and green-opsin, blue-opsin, and UV-opsin signals were unchanged, despite co-expressed red opsins, and the finding that an sws1 UV-opsin reporter gene was shut down by the gnat2:mYFP-2A-trß2 transgene. By contrast both LWS2 red-cone amplitudes and the density of red-cone immunoreactivity more than doubled in 5-dpf crx:mYFP-2A-trß2 embryos, while UV-cone amplitudes were reduced 90%. Embryonic cones with trß2 gain-of-function transgenes were morphologically distinct from control red, blue or UV cones, with wider inner segments and shorter axons than red cones, suggesting cone spectral specification, opsin immunoreactivity and shape are influenced by the abundance and developmental timing of trß2 expression.

Thyroid Gene Mutations in Pregnant and Breastfeeding Women Diagnosed With Transient Congenital Hypothyroidism: Implications for the Offspring's Health.

Fetus and infants require appropriate thyroid hormone levels and iodine during pregnancy and lactation. Nature endorses the mother to supply thyroid hormones to the fetus and iodine to the lactating infant. Genetic variations on thyroid proteins that cause dyshormonogenic congenital hypothyroidism could in pregnant and breastfeeding women impair the delivery of thyroid hormones and iodine to the offspring. The review discusses maternal genetic variations in thyroid proteins that, in the context of pregnancy and/or breastfeeding, could trigger thyroid hormone deficiency or iodide transport defect that will affect the proper development of the offspring.

The decrease of T3 / T4 is not hypothyroidism - a new mutation of Serpina7 gene results in partial thyroglobulin deficiency.

To explore an unusual cause of the decrease of T3/T4 through a new mutation of TBG gene in a family, so as to avoid habitual thinking and reduce subsequent over treatment. TSH, free total T4, T3 and free T4, T3 were determined by automatic chemiluminescence immunoassay. The TBG mutation was identified by direct DNA sequencing. A frameshift mutation of p. l372ffs * 32 was found in the TBG gene (c.1114delc) of the patient by direct DNA sequencing, and the proband of the family was heterozygous. In vitro expression showed that the affinity of TBG for T4 decreased. Further examination of the family members showed that T3 and T4 were decreased, while FT3, FT4 and TSH were normal. If the patients with low TT4 and TT3 but normal TSH are found, the serum TBG level and related genes should be detected to determine whether it is TBG deficiency and avoid wrong treatment.

Variation in Normal Range Thyroid Function Affects Serum Cholesterol Levels, Blood Pressure, and Type 2 Diabetes Risk: A Mendelian Randomization Study.

Background: Observational studies have demonstrated that variation in normal range thyroid function is associated with major cardiovascular risk factors, including dyslipidemia, hypertension, type 2 diabetes (T2D), and obesity. As observational studies are prone to residual confounding, reverse causality, and selection bias, we used a Mendelian randomization (MR) approach to investigate whether these associations are causal or not. Methods: Two-sample MR analysis using data from the largest available genome-wide association studies on normal range thyrotropin (TSH) and free thyroxine (fT4) levels, serum lipid levels, blood pressure measurements, T2D, and obesity traits (body mass index [BMI] and waist/hip ratio). Results: A one standard deviation (SD) increase in genetically predicted TSH levels was associated with a 0.037 SD increase in total cholesterol levels (p = 3.0 × 10-4). After excluding pleiotropic instruments, we also observed significant associations between TSH levels and low-density lipoprotein levels (ß = 0.026 SD, p = 1.9 × 10-3), pulse pressure (ß = -0.477 mmHg, p = 7.5 × 10-10), and T2D risk (odds ratio = 0.95, p = 2.5 × 10-3). While we found no evidence of causal associations between TSH or fT4 levels and obesity traits, we found that a one SD increase in genetically predicted BMI was associated with a 0.075 SD decrease in fT4 levels (p = 3.6 × 10-4). Conclusions: Variation in normal range thyroid function affects serum cholesterol levels, blood pressure, and T2D risk.

Interplay between Thyroid Hormones and Stearoyl-CoA Desaturase 1 in the Regulation of Lipid Metabolism in the Heart.

Stearoyl-CoA desaturase 1 (SCD1), an enzyme that is involved in the biosynthesis of monounsaturated fatty acids, induces the reprogramming of cardiomyocyte metabolism. Thyroid hormones (THs) activate both lipolysis and lipogenesis. Many genes that are involved in lipid metabolism, including Scd1, are regulated by THs. The present study used SCD1 knockout (SCD1-/-) mice to test the hypothesis that THs are important factors that mediate the anti-steatotic effect of SCD1 downregulation in the heart. SCD1 deficiency decreased plasma levels of thyroid-stimulating hormone and thyroxine and the expression of genes that regulate intracellular TH levels (i.e., Slc16a2 and Dio1-3) in cardiomyocytes. Both hypothyroidism and SCD1 deficiency affected genomic and non-genomic TH pathways in the heart. SCD1 deficiency is known to protect mice from genetic- or diet-induced obesity and decrease lipid content in the heart. Interestingly, hypothyroidism increased body adiposity and triglyceride and diacylglycerol levels in the heart in SCD1-/- mice. The accumulation of triglycerides in cardiomyocytes in SCD1-/- hypothyroid mice was caused by the activation of lipogenesis, which likely exceeded the upregulation of lipolysis and fatty acid oxidation. Lipid accumulation was also observed in the heart in wildtype hypothyroid mice compared with wildtype control mice, but this process was related to a reduction of triglyceride lipolysis and fatty acid oxidation. We also found that simultaneous SCD1 and deiodinase inhibition increased triglyceride content in HL-1 cardiomyocytes, and this process was related to the downregulation of lipolysis. Altogether, the present results suggest that THs are an important part of the mechanism of SCD1 in cardiac lipid utilization and may be involved in the upregulation of energetic metabolism that is associated with SCD1 deficiency.

AATF and SMARCA2 are associated with thyroid volume in Hashimoto's thyroiditis patients.

Thyroid volume of Hashimoto's thyroiditis (HT) patients varies in size over the course of disease and it may reflect changes in biological function of thyroid gland. Patients with subclinical hypothyroidism predominantly have increased thyroid volume whereas patients with more pronounced hypothyroidism have smaller thyroid volumes. Suggested mechanism for thyroid atrophy is thyrocyte death due to apoptosis. We performed the first genome-wide association study (GWAS) of thyroid volume in two groups of HT patients, depending on levothyroxine (LT4) therapy, and then meta-analysed across. Study included 345 HT patients in total and 6 007 322 common autosomal genetic variants. Underlying hypothesis was that genetic components that are involved in regulation of thyroid volume display their effect in specific pathophysiologic conditions of thyroid gland of HT patients. We additionally performed immunohistochemical analysis using thyroid tissues and analysed differences in expression levels of identified proteins and apoptotic marker between HT patients and controls. We found genome-wide significant association of two loci, both involved in apoptosis, with thyroid volume of HT patients: rs7212416 inside apoptosis-antagonizing transcription factor AATF (P = 8.95 × 10-9) and rs10738556 near chromatin-remodeling SMARCA2 (P = 2.83 × 10-8). In immunohistochemical analysis we observed that HT patients with homozygous AATF risk genotypes have decreased AATF expression (0.46-fold, P < 0.0001) and increased apoptosis (3.99-fold, P = 0.0001) in comparison to controls. HT patients with heterozygous SMARCA2 genotypes have decreased SMARCA2 expression, albeit without reaching statistical significance (1.07-fold, P = 0.5876), and significantly increased apoptosis (4.11-fold, P < 0.0001). By two lines of evidence we show that two highly plausible genetic loci, AATF and SMARCA2, may be involved in determining the thyroid volume of HT patients. The results of our study significantly add to the current knowledge of disturbed biological mechanisms in thyroid gland of HT patients.

Age-Related Resistance to Thyroid Hormone Action.

The age-related resistance to thyroid hormones (THs) explains the paucity of symptoms and signs of hyperthyroidism in older adults and may partly explain the myriad of symptoms and signs of hypothyroidism in biochemically euthyroid older people. This review considers the available data on the mechanisms underlying TH resistance with aging and compares these physiologic changes with the changes observed in congenital TH resistance syndromes. Aging is associated with alterations in TH economy along with a host of changes in the responsiveness of various tissues to THs. The age-related resistance to THs can be attributed to decreased TH transport to tissues, decreased nuclear receptor occupancy, decreased activation of thyroxine to triiodothyronine, and alterations in TH responsive gene expression. Although an increase in serum TH levels is expected in syndromes of TH resistance, unchanged serum TH levels in the euthyroid elderly is the result of increased sensitivity to TH negative feedback with increased suppression of thyroid-stimulating hormone, decreased thyroidal sensitivity to thyroid-stimulating hormone, and decreased TH production and secretion. The current clinical evidence suggests that the age-related TH resistance is mostly an adaptive response of the aging organism. It is tempting to speculate that similar changes can occur prematurely in a group of younger people who present with signs and symptoms of hypothyroidism despite normal serum thyroid function tests.

The role of thyroglobulin in thyroid hormonogenesis.

In humans, the thyroid hormones T3 and T4 are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T4 and T3 at distinct sites. T4 formation involves oxidative coupling between two DIT side chains, and de novo T3 formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T3 formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

Insight Into Molecular Determinants of T3 vs T4 Recognition From Mutations in Thyroid Hormone Receptor α and ß.

CONTEXT: The two major forms of circulating thyroid hormones (THs) are T3 and T4. T3 is regarded as the biologically active hormone because it binds to TH receptors (TRs) with greater affinity than T4. However, it is currently unclear what structural mechanisms underlie this difference in affinity. OBJECTIVE: Prompted by the identification of a novel M256T mutation in a resistance to TH (RTH)α patient, we investigated Met256 in TRα1 and the corresponding residue (Met310) in TRß1, residues previously predicted by crystallographic studies in discrimination of T3 vs T4. METHODS: Clinical characterization of the RTHα patient and molecular studies (in silico protein modeling, radioligand binding, transactivation, and receptor-cofactor studies) were performed. RESULTS: Structural modeling of the TRα1-M256T mutant showed that distortion of the hydrophobic niche to accommodate the outer ring of ligand was more pronounced for T3 than T4, suggesting that this substitution has little impact on the affinity for T4. In agreement with the model, TRα1-M256T selectively reduced the affinity for T3. Also, unlike other naturally occurring TRα mutations, TRα1-M256T had a differential impact on T3- vs T4-dependent transcriptional activation. TRα1-M256A and TRß1-M310T mutants exhibited similar discordance for T3 vs T4. CONCLUSIONS: Met256-TRα1/Met310-TRß1 strongly potentiates the affinity of TRs for T3, thereby largely determining that T3 is the bioactive hormone rather than T4. These observations provide insight into the molecular basis for underlying the different affinity of TRs for T3 vs T4, delineating a fundamental principle of TH signaling.

Genome-wide association meta-analysis for total thyroid hormone levels in Croatian population.

Thyroid hormones (THs) are key regulators of cellular growth, development, and metabolism. The thyroid gland secretes two THs, thyroxine (T4) and triiodothyronine (T3), into the plasma where they are almost all bound reversibly to plasma proteins. Free forms of THs are metabolically active, however, they represent a very small fraction of total TH levels. No genome-wide studies have been performed to date on total TH levels, comprising of protein-bound and free forms of THs. To detect genetic variants associated with total TH levels, we carried out the first GWAS meta-analysis of total T4 levels in 1121 individuals from two Croatian cohorts (Split and Korcula). We also performed GWAS analyses of total T3 levels in 577 individuals and T3/T4 ratio in 571 individuals from the Split cohort. The top association in GWAS meta-analysis of total T4 was detected for an intronic variant within SLC22A9 gene (rs12282281, P = 4.00 × 10-7). Within the same region, a genome-wide significant variant (rs11822642, P = 2.50 × 10-8) for the T3/T4 ratio was identified. SLC22A9 encodes for an organic anion transporter protein expressed predominantly in the liver and belongs to the superfamily of solute carriers (SLC), a large group of transport membrane proteins. The transport of THs across the plasma membrane in peripheral tissues is facilitated by the membrane proteins, and all TH transport proteins known to date belong to the same SLC superfamily as SLC22A9. These results suggest a potential role for SLC22A9 as a novel transporter protein of THs.

TDP-43 proteinopathy in aging: Associations with risk-associated gene variants and with brain parenchymal thyroid hormone levels.

TDP-43 proteinopathy is very prevalent among the elderly (affecting at least 25% of individuals over 85 years of age) and is associated with substantial cognitive impairment. Risk factors implicated in age-related TDP-43 proteinopathy include commonly inherited gene variants, comorbid Alzheimer's disease pathology, and thyroid hormone dysfunction. To test parameters that are associated with aging-related TDP-43 pathology, we performed exploratory analyses of pathologic, genetic, and biochemical data derived from research volunteers in the University of Kentucky Alzheimer's Disease Center autopsy cohort (n = 136 subjects). Digital pathologic methods were used to discriminate and quantify both neuritic and intracytoplasmic TDP-43 pathology in the hippocampal formation. Overall, 46.4% of the cases were positive for TDP-43 intracellular inclusions, which is consistent with results in other prior community-based cohorts. The pathologies were correlated with hippocampal sclerosis of aging (HS-Aging) linked genotypes. We also assayed brain parenchymal thyroid hormone (triiodothyronine [T3] and thyroxine [T4]) levels. In cases with SLCO1A2/IAPP or ABCC9 risk associated genotypes, the T3/T4 ratio tended to be reduced (p = .051 using 2-tailed statistical test), and in cases with low T3/T4 ratios (bottom quintile), there was a higher likelihood of HS-Aging pathology (p = .025 using 2-tailed statistical test). This is intriguing because the SLCO1A2/IAPP and ABCC9 risk associated genotypes have been associated with altered expression of the astrocytic thyroid hormone receptor (protein product of the nearby gene SLCO1C1). These data indicate that dysregulation of thyroid hormone signaling may play a role in age-related TDP-43 proteinopathy.

Assessment of the Relationship Between Genetic Determinants of Thyroid Function and Atrial Fibrillation: A Mendelian Randomization Study.

Importance: Increased free thyroxine (FT4) and decreased thyrotropin are associated with increased risk of atrial fibrillation (AF) in observational studies, but direct involvement is unclear. Objective: To evaluate the potential direct involvement of thyroid traits on AF. Design, Setting, and Participants: Study-level mendelian randomization (MR) included 11 studies, and summary-level MR included 55 114 AF cases and 482 295 referents, all of European ancestry. Exposures: Genomewide significant variants were used as instruments for standardized FT4 and thyrotropin levels within the reference range, standardized triiodothyronine (FT3):FT4 ratio, hypothyroidism, standardized thyroid peroxidase antibody levels, and hyperthyroidism. Mendelian randomization used genetic risk scores in study-level analysis or individual single-nucleotide polymorphisms in 2-sample MR for the summary-level data. Main Outcomes and Measures: Prevalent and incident AF. Results: The study-level analysis included 7679 individuals with AF and 49 233 referents (mean age [standard error], 62 [3] years; 15 859 men [29.7%]). In study-level random-effects meta-analysis, the pooled hazard ratio of FT4 levels (nanograms per deciliter) for incident AF was 1.55 (95% CI, 1.09-2.20; P = .02; I2 = 76%) and the pooled odds ratio (OR) for prevalent AF was 2.80 (95% CI, 1.41-5.54; P = .003; I2 = 64%) in multivariable-adjusted analyses. The FT4 genetic risk score was associated with an increase in FT4 by 0.082 SD (standard error, 0.007; P < .001) but not with incident AF (risk ratio, 0.84; 95% CI, 0.62-1.14; P = .27) or prevalent AF (OR, 1.32; 95% CI, 0.64-2.73; P = .46). Similarly, in summary-level inverse-variance weighted random-effects MR, gene-based FT4 within the reference range was not associated with AF (OR, 1.01; 95% CI, 0.89-1.14; P = .88). However, gene-based increased FT3:FT4 ratio, increased thyrotropin within the reference range, and hypothyroidism were associated with AF with inverse-variance weighted random-effects OR of 1.33 (95% CI, 1.08-1.63; P = .006), 0.88 (95% CI, 0.84-0.92; P < .001), and 0.94 (95% CI, 0.90-0.99; P = .009), respectively, and robust to tests of horizontal pleiotropy. However, the subset of hypothyroidism single-nucleotide polymorphisms involved in autoimmunity and thyroid peroxidase antibodies levels were not associated with AF. Gene-based hyperthyroidism was associated with AF with MR-Egger OR of 1.31 (95% CI, 1.05-1.63; P = .02) with evidence of horizontal pleiotropy (P = .045). Conclusions and Relevance: Genetically increased FT3:FT4 ratio and hyperthyroidism, but not FT4 within the reference range, were associated with increased AF, and increased thyrotropin within the reference range and hypothyroidism were associated with decreased AF, supporting a pathway involving the pituitary-thyroid-cardiac axis.

The Role of Transforming Growth Factor-ß1 Gene Polymorphism and Its Serum Levels in Hashimoto's Thyroiditis.

BACKGROUND: TGF-ß1 gene (TGFB1) is one of the target genes involved in genetic predisposition to autoimmune diseases, particularly Hashimoto's thyroiditis (HT). OBJECTIVE: In the present study, we attempted to investigate whether -509C/T SNP (rs1800469) in the promoter of TGFB1 is associated with the genetic susceptibility and clinical characteristics of Bulgarian patients with HT. We also analyzed serum TGF-ß1 levels in different stages of the disease and its association with the -509C/T polymorphism in the TGFB1 promoter. METHODS: The study recruited 121 female out-patients with autoimmune thyroiditis and 250 agematched healthy women (HC). Genotyping of the rs1800469 was performed by restriction fragment length polymorphism (RFLP)-PCR assay. The serum concentrations of latent acid-activated TGF-ß1 protein were determined by the quantitative sandwich ELISA method. RESULTS: Upon testing different types of inheritance, a significant risk was found for heterozygotes (CT) with OR=1.640; p=0.05 under the codominant model. The significantly higher risk for developing Hypothyroidism was calculated again for CT-genotype patients with OR=1.789. According to the hormone reference values, a significant association of CT genotype with decreased TSH (75.4%) simultaneously with increased free T4 hormone (94%) levels was also calculated. When patients were stratified by genotype and compared to the same genotype in HC, we observed that the decreased levels in serum TGF-b1 were significant for patients who carried the C-allele in their genotype. CONCLUSION: We suggest that heterozygous genotype CT is a genetic risk factor for developing more severe HT due to enhanced free T4 serum level at the onset of the disease, before developing the hypothyroid stage.