Thyroid Hormone Receptor Beta Research Articles

MetALD: Does it require a different therapeutic option?

New guidelines for the definitions of steatotic liver disease have named the entity of MetALD as an overlap condition of metabolic-dysfunction associated steatotic liver disease (MASLD) and alcohol-related liver disease. There is a broad range of therapeutics in all stages of development for MASLD but these therapeutics in general have not been studied in patients with significant ongoing alcohol use. In this review we discuss the current understanding of the endogenous and exogenous risks for MASLD and MetALD. Rational strategies for therapeutic intervention in MetALD include biopsychosocial interventions, alcohol use cessation strategies including the use of medications for alcohol use disorder and judicious use of therapeutics for steatotic liver disease. Therapeutics with promise for MetALD include incretin-based therapies, fibroblast growth factor 21 (FGF21) agonists, thyroid hormone receptor beta (THR- β) agonists, sodium-glucose co-transporter 2 (SGLT2) inhibitors and agents to modify de-novo lipogenesis (DNL). Currently glucagon like peptide 1 receptor agonists (GLP-1ra) and peroxisome proliferator-activated receptor (PPAR) γ agonists have the largest body of literature supporting their use in MASLD and there is a paucity of agents in trials for alcohol-related liver disease. From existing studies, it is not clear if unique therapeutics or a combinatorial approach are needed for MetALD. Further elucidation of the safety and benefits of MASLD-related therapies are of paramount importance for advancing therapeutics for MetALD in carefully designed inclusive clinical trials.

Effects of penthiopyrad on the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish

Exposure to specific pesticides has been demonstrated to alter normal thyroid function of aquatic vertebrates. This study aimed to investigate the impact of penthiopyrad (PO) on the thyroid function of zebrafish, further elucidating its toxic mechanisms on the early developmental stages of zebrafish. Exposure to sublethal doses of PO (0.3–1.2 mg/L) for 8 days from 2 h after fertilization resulted in a significant reduction in larval swim bladder size and body weight, accompanied by developmental abnormalities such as pigment deposition and abnormal abdominal development. Perturbations in the hypothalamic-pituitary-thyroid (HPT) axis in larvae manifested as a marked upregulation of crh, tg, ttr, and ugt1ab expression, alongside downregulation of trβ expression, culminating in elevated thyroxine (T4) and triiodothyronine (T3) levels. Additionally, molecular docking results suggest that PO and its metabolites may disrupt the binding of thyroid hormones to thyroid hormone receptor beta (TRβ), compromising the normal physiological function of TRβ. These findings highlight the PO-induced adverse effects on the HPT axis of larvae under sublethal doses, eventually leading to abnormal development and growth inhibition.

Resmetirom (Rezdiffra) for metabolic dysfunction-associated steatohepatitis.

Resmetirom (Rezdiffra – Madrigal), a thyroid hormone receptor-beta agonist, has received accelerated approval from the FDA for treatment of noncirrhotic nonalcoholic steatohepatitis (NASH) with moderate to advanced fibrosis in adults.

Pituitary Hyperplasia and Overt Hypothyroidism Induced by Methimazole in an Adolescent Girl with Resistance to Thyroid Hormone Accompanying Hashimoto’s Thyroiditis: A Case Report

We describe a 13-year-old girl who presented at her local hospital with a diffuse goiter and had discrepant thyroid function test (TFT) of elevated free T4 (FT4), free T3 (FT3) levels with mildly elevated thyroid-stimulating hormone (TSH) and a pituitary magnetic resonance imaging (MRI) report of a pituitary hyperplasia. She was referred to our hospital where a repeat TFT found low FT4 and high TSH levels, and high levels of antithyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-TG) antibodies, leading to the diagnosis of Hashimoto’s thyroiditis (HT) with overt primary hypothyroidism. The girl had a good response after daily 100 µg levothyroxine treatment for 8 months with decreased goiter size along with disappearance of the pituitary mass. However, her FT4 and FT3 levels were elevated while the TSH was in the high normal range, although at this time there were no signs of hyperthyroidism. A genetic study confirmed our provisional diagnosis that the patient had a p.Pro453Thr monoallelic loss-of-function mutation of the thyroid hormone receptor beta (THRB) gene, suggesting the diagnosis of coexisting resistance to thyroid hormone-β (RTHβ) and HT in this patient.

Identification of hot spots and co-occurrence patterns of activities on thyroid hormone receptor and transthyretin binding in passive samplers from Czech surface waters

One of the less studied in vitro biological activities in the aquatic environment are thyroid hormone receptor beta (TRβ)-mediated agonistic and antagonistic activities and transthyretin (TTR) binding activity. They were measured mostly using active sampling methods, but rarely found. It is unclear if these activities co-occur, and the drivers of the (anti-)TRβ activity are mostly unknown. Therefore, the main aim of the study was to determine (anti-)TRβ activities as well as transthyretin (TTR) binding activity in passive samplers from Czech surface waters in combination with the search for the effect drivers based on liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis by applying suspect screening. Passive samplers (polar organic chemical integrative samplers, POCIS) were deployed at twenty-one sites (all ends of watersheds and other important sites in Elbe River) in the Czech rivers. The (anti-)TRβ and TTR binding activity were measured using (anti-)TRβ-CALUX and TTR-TRβ-CALUX bioassays. Anti-TRβ activity was found at eight sites, and TTR binding activity co-occurred there at six of these sites. The co-occurrence of TRβ-mediated antagonistic activity and TTR binding indicate that they may have common effect drivers. No sample exhibited TRβ agonistic activity. The extract from the site Bílina River, the most burdened with anti-TRβ activity, was further successfully fractionated, and this activity was revealed in the fraction, where mid-polar compounds prevailed. However, the suspect LC-HRMS analysis did not reveal the chemical effect drivers. Our results showed that anti-TRβ activity can be found in surface waters by employing passive sampling and frequently co-occurs with TTR binding activity. Overall, the fractionation procedure and non-target data acquisition used in this study can serve as a basis for searching the effect drivers in future research.

Identification of relevant differential genes to the divergent development of pectoral muscle in ducks by transcriptomic analysis.

The objective of this study was to identify candidate genes that play important roles in skeletal muscle development in ducks. In this study, we investigated the transcriptional sequencing of embryonic pectoral muscles from two specialized lines: Liancheng white ducks (female) and Cherry valley ducks (male) hybrid Line A (LCA) and Line C (LCC) ducks. In addition, prediction of target genes for the differentially expressed mRNAs was conducted and the enriched gene ontology (GO) terms and Kyoto encyclopedia of genes and genomes signaling pathways were further analyzed. Finally, a protein-to-protein interaction network was analyzed by using the target genes to gain insights into their potential functional association. A total of 1,428 differentially expressed genes (DEGs) with 762 being up-regulated genes and 666 being down-regulated genes in pectoral muscle of LCA and LCC ducks identified by RNA-seq (p<0.05). Meanwhile, 23 GO terms in the down-regulated genes and 75 GO terms in up-regulated genes were significantly enriched (p<0.05). Furthermore, the top 5 most enriched pathways were ECM-receptor interaction, fatty acid degradation, pyruvate degradation, PPAR signaling pathway, and glycolysis/gluconeogenesis. Finally, the candidate genes including integrin b3 (Itgb3), pyruvate kinase M1/2 (Pkm), insulinlike growth factor 1 (Igf1), glucose-6-phosphate isomerase (Gpi), GABA type A receptorassociated protein-like 1 (Gabarapl1), and thyroid hormone receptor beta (Thrb) showed the most expression difference, and then were selected to verification by quantitative realtime polymerase chain reaction (qRT-PCR). The result of qRT-PCR was consistent with that of transcriptome sequencing. This study provided information of molecular mechanisms underlying the developmental differences in skeletal muscles between specialized duck lines.

Challenging diagnosis of resistance to thyroid hormone in a patient with COVID-19, pituitary microadenoma and unusual response to octreotide long-acting release test.

The resistance to thyroid hormone syndrome (RTHβ) occurs uncommonly and requires a high level of clinical suspicion and specific investigations to reach a precise diagnosis and to avoid unnecessary and potentially harmful therapies. We report a case of a young male patient referred to our unit for SARS-CoV-2 infection and atrial fibrillation with elevated thyroid hormones and non-suppressed thyroid-stimulating hormone (TSH), for which antithyroid therapy was prescribed. A mood disorder was reported in the medical history. The family history was unknown as the patient was adopted. Thyroid-specific antibodies were undetectable, and thyroid ultrasound revealed a normal thyroid gland without nodules. After the resolution of SARS-CoV-2 infection, the diagnostic workup continued, and the pituitary MRI revealed a small area ascribable to a microadenoma. Due to atrial fibrillation, the execution of the T3 test was contraindicated. The octreotide long-acting release (LAR) test showed an initial reduction of free thyroid hormones levels at first administration, which was consistent with the presence of a TSH-secreting pituitary tumour, although an escape from the response was observed after the following two injections of octreotide LAR. Indeed, the genetic investigation revealed a variant in heterozygosity of the THRβ gene (Pro453Ser), thus leading to an RTHβ diagnosis, and, therefore, medical treatment with triiodothyroacetic acid was initiated. After 2 years from the SARS-CoV-2 infection, the patient continues the follow-up at our outpatient clinic, and no other medical interventions are needed. RTHβ is a rare genetic syndrome characterised by discrepant thyroid function tests and by a dissociation between the observed hormone levels and the expected patient signs and symptoms. Features of thyroid hormone deficiency in TR-ß dependent tissues (pituitary gland, hypothalamus, liver and neurosensitive epithelia), as well as thyroid hormone excess in TR-α-dependent tissues (heart, bone, skeletal muscle and brain), may coexist in the same individual. Clinical pictures can be different even when the same variant occurs, suggesting that other genetic and/or epigenetic factors may play a role in determining the patient's phenotype. Differentiating RTHβ from a TSH-secreting pituitary tumour is very difficult, especially when a concomitant pituitary adenoma is detected during diagnostic workup. The injection of long-acting somatostatin analogues can help differentiate the two conditions, but it is important to detect any interference in the dosage of thyroid hormones to avoid an incorrect diagnosis. Genetic testing is fundamental to prevent unnecessary and potentially harmful therapies. Medical treatment with triiodothyroacetic acid was demonstrated to be effective in reducing thyroid hormone excess and controlling symptoms.

Truncated variants of thyroid hormone receptor beta display disease-inflicting malfunctioning at cellular level

Thyroid hormone receptor β (THRβ) is a member of the nuclear receptor superfamily of ligand-modulated transcription factors. Upon ligand binding, THRβ sequentially recruits the components of transcriptional machinery to modulate target gene expression. In addition to regulating diverse physiological processes, THRβ plays a crucial role in hypothalamus-pituitary-thyroid axis feedback regulation. Anomalies in THRβ gene/protein structure are associated with onset of diverse disease states. In this study, we investigated disease-inflicting truncated variants of THRβ using in-silico analysis and cell-based assays. We examined the THRβ truncated variants on multiple test parameters, including subcellular localization, ligand-receptor interactions, transcriptional functions, interaction with heterodimeric partner RXR, and receptor-chromatin interactions. Moreover, molecular dynamic simulation approaches predicted that shortened THRβ-LBD due to point mutations contributes proportionally to the loss of structural integrity and receptor stability. Deviant subcellular localization and compromised transcriptional function were apparent with these truncated variants. Present study shows that ‘mitotic bookmarking’ property of some THRβ variants is also affected. The study highlights that structural and conformational attributes of THRβ are necessary for normal receptor functioning, and any deviations may contribute to the underlying cause of the inflicted diseases. We anticipate that insights derived herein may contribute to improved mechanistic understanding to assess disease predisposition.

HINT2 protects against pressure overload-induced cardiac remodelling through mitochondrial pathways.

Histidine triad nucleotide-binding protein 2 (HINT2) is an enzyme found in mitochondria that functions as a nucleotide hydrolase and transferase. Prior studies have demonstrated that HINT2 plays a crucial role in ischemic heart disease, but its importance in cardiac remodelling remains unknown. Therefore, the current study intends to determine the role of HINT2 in cardiac remodelling. HINT2 expression levels were found to be lower in failing hearts and hypertrophy cardiomyocytes. The mice that overexpressed HINT2 exhibited reduced myocyte hypertrophy and cardiac dysfunction in response to stress. In contrast, the deficiency of HINT2 in the heart of mice resulted in a worsening hypertrophic phenotype. Further analysis indicated that upregulated genes were predominantly associated with the oxidative phosphorylation and mitochondrial complex I pathways in HINT2-overexpressed mice after aortic banding (AB) treatment. This suggests that HINT2 increases the expression of NADH dehydrogenase (ubiquinone) flavoprotein (NDUF) genes. In cellular studies, rotenone was used to disrupt mitochondrial complex I, and the protective effect of HINT2 overexpression was nullified. Lastly, we predicted that thyroid hormone receptor beta might regulate HINT2 transcriptional activity. To conclusion, the current study showcased that HINT2 alleviates pressure overload-induced cardiac remodelling by influencing the activity and assembly of mitochondrial complex I. Thus, targeting HINT2 could be a novel therapeutic strategy for reducing cardiac remodelling.

A Phase 3, Randomized, Controlled Trial of Resmetirom in NASH with Liver Fibrosis

BackgroundNonalcoholic steatohepatitis (NASH) is a progressive liver disease with no approved treatment. Resmetirom is an oral, liver-directed, thyroid hormone receptor beta–selective agonist in development for the treatment of NASH with liver fibrosis.MethodsWe are conducting an ongoing phase 3 trial involving adults with biopsy-confirmed NASH and a fibrosis stage of F1B, F2, or F3 (stages range from F0 [no fibrosis] to F4 [cirrhosis]). Patients were randomly assigned in a 1:1:1 ratio to receive once-daily resmetirom at a dose of 80 mg or 100 mg or placebo. The two primary end points at week 52 were NASH resolution (including a reduction in the nonalcoholic fatty liver disease [NAFLD] activity score by ≥2 points; scores range from 0 to 8, with higher scores indicating more severe disease) with no worsening of fibrosis, and an improvement (reduction) in fibrosis by at least one stage with no worsening of the NAFLD activity score.ResultsOverall, 966 patients formed the primary analysis population (322 in the 80-mg resmetirom group, 323 in the 100-mg resmetirom group, and 321 in the placebo group). NASH resolution with no worsening of fibrosis was achieved in 25.9% of the patients in the 80-mg resmetirom group and 29.9% of those in the 100-mg resmetirom group, as compared with 9.7% of those in the placebo group (P<0.001 for both comparisons with placebo). Fibrosis improvement by at least one stage with no worsening of the NAFLD activity score was achieved in 24.2% of the patients in the 80-mg resmetirom group and 25.9% of those in the 100-mg resmetirom group, as compared with 14.2% of those in the placebo group (P<0.001 for both comparisons with placebo). The change in low-density lipoprotein cholesterol levels from baseline to week 24 was −13.6% in the 80-mg resmetirom group and −16.3% in the 100-mg resmetirom group, as compared with 0.1% in the placebo group (P<0.001 for both comparisons with placebo). Diarrhea and nausea were more frequent with resmetirom than with placebo. The incidence of serious adverse events was similar across trial groups: 10.9% in the 80-mg resmetirom group, 12.7% in the 100-mg resmetirom group, and 11.5% in the placebo group.ConclusionsBoth the 80-mg dose and the 100-mg dose of resmetirom were superior to placebo with respect to NASH resolution and improvement in liver fibrosis by at least one stage. (Funded by Madrigal Pharmaceuticals; MAESTRO-NASH ClinicalTrials.gov number, NCT03900429.)

Hypothalamic Thyroid Hormone Receptor α1 Signaling Controls Body Temperature.

Background: The importance of thyroid hormones (THs) for peripheral body temperature regulation has been long recognized, as medical conditions such as hyper- and hypothyroidism lead to alterations in body temperature and energy metabolism. In the past decade, the brain actions of THs and their respective nuclear receptors, thyroid hormone receptor α1 (TRα1) and thyroid hormone receptor beta (TRβ), coordinating body temperature regulation have moved into focus. However, the exact roles of the individual TR isoforms and their precise neuroanatomical substrates remain poorly understood. Methods: Here we used mice expressing a mutant TRα1 (TRα1+m) as well as TRβ knockouts to study body temperature regulation using radiotelemetry in conscious and freely moving animals at different ambient temperatures, including their response to oral 3,3',5-triiodothyronine (T3) treatment. Subsequently, we tested the effects of a dominant-negative TRα1 on body temperature after adeno-associated virus (AAV)-mediated expression in the hypothalamus, a region known to be involved in thermoregulation. Results: While TRβ seems to play a negligible role in body temperature regulation, TRα1+m mice had lower body temperature, which was surprisingly not entirely normalized at 30°C, where defects in facultative thermogenesis or tail heat loss are eliminated as confounding factors. Only oral T3 treatment fully normalized the body temperature profile of TRα1+m mice, suggesting that the mutant TRα1 confers an altered central temperature set point in these mice. When we tested this hypothesis more directly by expressing the dominant-negative TRα1 selectively in the hypothalamus via AAV transfection, we observed a similarly reduced body temperature at room temperature and 30°C. Conclusion: Our data suggest that TRα1 signaling in the hypothalamus is important for maintaining body temperature. However, further studies are needed to dissect the precise neuroanatomical substrates and the downstream pathways mediating this effect.

The thyroid hormone enhances mouse embryonic fibroblasts reprogramming to pluripotent stem cells: role of the nuclear receptor corepressor 1.

Pluripotent stem cells can be generated from somatic cells by the Yamanaka factors Oct4, Sox2, Klf4 and c-Myc. Mouse embryonic fibroblasts (MEFs) were transduced with the Yamanaka factors and generation of induced pluripotent stem cells (iPSCs) was assessed by formation of alkaline phosphatase positive colonies, pluripotency gene expression and embryod bodies formation. The thyroid hormone triiodothyronine (T3) enhances MEFs reprogramming. T3-induced iPSCs resemble embryonic stem cells in terms of the expression profile and DNA methylation pattern of pluripotency genes, and of their potential for embryod body formation and differentiation into the three major germ layers. T3 induces reprogramming even though it increases expression of the cyclin kinase inhibitors p21 and p27, which are known to oppose acquisition of pluripotency. The actions of T3 on reprogramming are mainly mediated by the thyroid hormone receptor beta and T3 can enhance iPSC generation in the absence of c-Myc. The hormone cannot replace Oct4 on reprogramming, but in the presence of T3 is possible to obtain iPSCs, although with low efficiency, without exogenous Klf4. Furthermore, depletion of the corepressor NCoR (or Nuclear Receptor Corepressor 1) reduces MEFs reprogramming in the absence of the hormone and strongly decreases iPSC generation by T3 and also by 9cis-retinoic acid, a well-known inducer of reprogramming. NCoR depletion also markedly antagonizes induction of pluripotency gene expression by both ligands. Inclusion of T3 on reprogramming strategies has a potential use in enhancing the generation of functional iPSCs for studies of cell plasticity, disease and regenerative medicine.

An integrated gene-to-outcome multimodal database for metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the commonest cause of chronic liver disease worldwide and represents an unmet precision medicine challenge. We established a retrospective national cohort of 940 histologically defined patients (55.4% men, 44.6% women; median body mass index 31.3; 32% with type 2 diabetes) covering the complete MASLD severity spectrum, and created a secure, searchable, open resource (SteatoSITE). In 668 cases and 39 controls, we generated hepatic bulk RNA sequencing data and performed differential gene expression and pathway analysis, including exploration of gender-specific differences. A web-based gene browser was also developed. We integrated histopathological assessments, transcriptomic data and 5.67 million days of time-stamped longitudinal electronic health record data to define disease-stage-specific gene expression signatures, pathogenic hepatic cell subpopulations and master regulator networks associated with adverse outcomes in MASLD. We constructed a 15-gene transcriptional risk score to predict future hepatic decompensation events (area under the receiver operating characteristic curve 0.86, 0.81 and 0.83 for 1-, 3- and 5-year risk, respectively). Additionally, thyroid hormone receptor beta regulon activity was identified as a critical suppressor of disease progression. SteatoSITE supports rational biomarker and drug development and facilitates precision medicine approaches for patients with MASLD.

FRI479 Resistance To Thyroid Hormone Due To Thyroid Hormone Receptor Alpha (THRA) Gene Mutation

Abstract Disclosure: J.O. Abdelkarim: None. S. Parveen: None. M.G. Jakoby: None. J. Fleischer: None. Introduction: Resistance to thyroid hormone (RTH) is a heritable disorder characterized by diminished response to triiodothyronine (T3). Most cases of RTH are due to mutations in the thyroid hormone receptor beta (THRB) gene (“RTH-beta”). Mutations in thyroid hormone receptor alpha (THRA) gene appear to be a rare cause of RTH (“RTH-alpha”), with the first case reported in 2012. We present a case of RTH-alpha in a patient confirmed to have a pathogenic THRA mutation. Clinical Case: A 38-year-old Caucasian male was referred to genetic clinic due to mild developmental delay, dyscalculia and mild autism spectrum disorder. He was born at term by uncomplicated spontaneous vaginal delivery. Parents first noticed developmental delays at age 5 y, though no evaluation occurred during childhood. As an adult, the patient completed seminary studies and was employed as a Catholic priest. An intellectual disability gene panel revealed a pathogenic variant of the THRA gene (c.1151G&amp;gt;A p.R384H). Both parents tested negative for the mutation. Examination was notable for obesity (183 cm, 186 kg, BMI 55.5), macrocephaly, hypertelorism, pectus excavatum and small hands with short digits. No thyroid anatomic thyroid abnormalities were appreciated on neck examination or ultrasonography. TSH was 1.860 mIU/L (0.358-3.740), free T4 0.71 ng/dL (0.76-1.46), and free T3 3.2 pg/mL (2.2-4.0). The patient had no symptoms of hypothyroidism, and supplemental thyroid hormone was deferred. Discussion: There are 29 reported THRA gene mutations and 32 cases of RTH-alpha reported in the peer reviewed literature. Common clinical features include mild-to-moderate intellectual impairment, low basal metabolic rate (BMR), mild skeletal dysplasia, normocytic anemia, bradycardia, consistent with high expression of THRA in brain, heart, gastrointestinal tract, skeletal muscle, and bone. TSH is normal to slightly increased, free T4 is low to low normal, and free T3 is normal to modestly elevated. This is the third reported case of the c.1151G&amp;gt;A missense mutation resulting in an arginine to histidine substitution at codon 384. Thyroid function tests conform to the pattern described for other cases of RTH-alpha. Like the other two patients with the R384H mutation, developmental delays occurred, though intellectual manifestations mitigated with time and the patient completed seminary studies without difficulty. Mitigation of phenotype with age has been reported in RTH-alpha mice with the R384C missense mutation. Short stature did not occur in this patient or the other R384H cases. Unlike other patients, this patient did not experience anemia or constipation. Macrocephaly is a common feature of the three R384H cases, but the patient’s other skeletal manifestations (e.g. pectus excavatum) were not reported. This case demonstrates the difficulty of recognizing THR-alpha and extends our understanding of the R384H phenotype. Presentation: Friday, June 16, 2023

OR14-06 Serum Thyroid Hormones Increase At The Onset Of Lactation And Promote Metabolic Pathways Required For Human Milk Synthesis

Abstract Disclosure: H. Rostom: None. X. Meng: None. R. Humphrey: None. A. Fry: None. T. Elajnaf: None. F. Hannan: None. An increase in mammary metabolism is critical for initiating lactation during postpartum days 1-4. We utilised clinical and cellular approaches to investigate whether thyroid hormones, which promote lactation in rodents, are involved in initiating human lactation and regulating mammary metabolism. We recruited n=35 healthy pregnant women intending to breastfeed following informed consent and measured serum thyroid hormones (TSH and free T4) at 36 weeks’ gestation and on postpartum days 1-4 (1). Serum TSH significantly increased at post-partum day 1 compared with 36 weeks’ gestation (2.5±0.3 vs. 1.6±0.1 mU/L, p=0.001). This early postpartum rise in TSH was followed by a significant increase in free T4 on post-partum days 3 and 4 (11.7±0.2 vs. 10.5±0.2pmol/L at 36 weeks’ gestation, p&amp;lt;0.01). We hypothesised that thyroid hormones increase mammary metabolism to promote breast milk production. Reverse transcription-quantitative PCR (RT-qPCR) of genes encoding deiodinase enzymes (DIO1-3), which regulate intracellular thyroid hormone activity, was undertaken in lactating human mammary epithelial cells (HMECs) isolated from breast milk. This showed that DIO1, which converts T4 to T3, was expressed in lactating HMECs, whereas DIO2 and DIO3 were not detected. Moreover, RT-qPCR of the thyroid hormone receptor alpha and beta (THRA and THRB) genes in lactating HMECs showed that THRB has ∼4-fold greater expression than THRA (p&amp;lt;0.05, n=4). THRB phosphorylates Akt, which is required for initiating lactation. Consistent with this, cultured HMECs stimulated with 10nM T3, the most potent thyroid hormone, for 15min showed an ∼2-fold increase in Akt phosphorylation (p&amp;lt;0.0001, n=4). Akt regulates oxidative phosphorylation, which we assessed by measuring oxygen consumption rate (OCR) and ATP synthesis. HMECs treated with 10nM T3 for ≤8hrs showed a 2-fold increase in OCR (p&amp;lt;0.05, n=4) without any change in cellular ATP. These findings suggested that T3 uncoupled mitochondrial respiration from ATP synthesis. In support of this, RT-qPCR of cultured HMECs stimulated with 10nM T3 showed increased expression of genes encoding uncoupling proteins 2 and 3 (≥2-fold, p&amp;lt;0.01, n=4), which also function to divert substrates away from mitochondrial catabolism; and &amp;gt;20-fold increased expression of PPARGC1A (p&amp;lt;0.0001, n=4), which promotes mitochondrial biogenesis. In summary, these findings demonstrate that serum TSH and free T4 are increased at the onset of lactation. Moreover, our cellular studies indicate that thyroid hormones promote mammary mitochondrial biogenesis and may divert substrates used for ATP generation towards the synthesis of breast milk. Reference: (1) Rostom, H. et al. Protocol for an observational study investigating hormones triggering the onset of sustained lactation: the INSIGHT study. BMJ Open 12, e062478. Presentation: Friday, June 16, 2023

OR14-03 The Thyroid Hormone Receptor Beta Genotype Of The Fetus Influences The Maternal Thyroid Function During Pregnancy

Abstract Disclosure: F. Salas Lucia: None. X. Liao: None. H. Jiang: None. A.M. Dumitrescu: None. S. Refetoff: None. J. Anselmo: None. When women with resistance to thyroid hormone beta (RTHβ) are pregnant, their high serum thyroid hormone (TH) levels are perceived as normal by affected fetuses (AfFe) carrying the same THRB mutation as their mothers. On the contrary, normal fetuses (NlFe) that do not carry the maternal THRB mutation are exposed to supraphysiologic TH levels and have unfavorable outcomes. This shows the impact maternal TH levels have on the fetus. However, whether the fetus might influence the maternal thyroid function remains unknown. To explore this possibility, we studied the maternal thyroid function tests (TFT) TSH, FT3, and FT4 throughout the pregnancies from 8 women harboring the R243Q THRB mutation (AfMo) during a total of 10 pregnancies: 6 carrying AfFe and 4 NlFe fetuses. Cord blood TFT from 3 of the NlFe and 3 AfFe at birth were also obtained. In addition, 8 pregnancies from 7 normal mothers (NlMo) carrying 4 AfFe who inherited the THRB mutation from the father and 4 NlFe were also evaluated for TFT. Cord blood from these pregnancies was not available. Results were compared to those in pregnancies of normal WT women. In all RTHβpregnancies, the maternal TSH values were within the range of pregnancies in WT women (0.35-4.94 mU/L) with an hCG-mediated nadir at the end of the first trimester. Maternal FT4 and FT3 values in RTHβpregnancies were above the upper limit of normal (ULN) of 100, peaking during weeks 5-16 (150±20% and 175±15% ULN, respectively) and progressively decreasing afterward. We found differences in maternal TFTdepending on the THRB genotype of the fetus. From weeks 25-32, the AfMo carrying an AfFe exhibited lower FT4 than when carrying a NlFe (96±2 vs. 108±5.3% ULN; p&amp;lt;0.05). Similarly, from weeks 25-40, the AfMo carrying an AfFe exhibited lower FT3 values than when carrying a NlFe ULN (110±11 vs. 134±13% ULN; p&amp;lt;0.05). While gestational age at delivery was similar in all RTHβ pregnancies, the NlFe had a lower birth body weight than the AfFe (2.3±0.1 vs. 3.1±0.2 kg; p&amp;lt;0.01). Cord blood TSH in NlFe was undetectable (&amp;lt;0.1 mU/L) but was 9.51 mU/L (2.2-10; range in normal neonates) in AfFe, which indicates that the thyroid function in NlFe could be restricted during pregnancy, but not in AfFe. Cord blood FT4 levels were similar in NlFe and AfFe (98.4±16.4 vs. 89.5±9.4% ULN). However, FT3 levels were significantly higher in NlFe than in AfFe (67.7±3.0 vs. 42.0±9.6% ULN; p&amp;lt;0.05) and represented ∼68, and ∼42% of the serum maternal FT3 level at birth, respectively. NlMo carrying either AfFe or NlFe showed similar TSH and FT3 levels during pregnancies. However, from weeks 33 to 40, FT4 levels were lower when carrying an AfFe than when carrying a NlFe (51.8±2.8 vs. 62.5±3.2% ULN; p&amp;lt;0.001). Our findings indicate that maternal thyroid function are influenced by THRB genotype of the fetus. The quantitation of placental and fetal TH transporters, deiodinases, and TH metabolites could provide insights into the mechanisms involved. Presentation: Friday, June 16, 2023

FRI472 Thyroid Hormone Resistance β (RTH- β) Syndrome In Patient With Multiple-system Atrophy Parkinsonian Type (MSA-P)

Abstract Disclosure: S. Lio: None. M. Albin: None. I. Campi: None. L. Persani: None. Background: Resistance to thyroid hormone β (RTHβ) is a rare dominantly inherited condition of impaired tissue responsiveness to thyroid hormones (TH) due to variants in the THRB gene encoding the TH receptor β (TRβ). RTHβ patients display a distinctive biochemical feature of central hyperthyroidism with elevated serum levels of FT3 and FT4 and unsuppressed TSH. Unfortunately, this syndrome is sometimes misdiagnosed as primary hyperthyroidism, with a delayed diagnosis or inappropriate treatments. Clinical Case: A 72-year-old lady was diagnosed elsewhere in 2010 with atrial fibrillation (AF) and parkinsonian multisystem atrophy (MSA-P), an orphan disease causing progressive autonomic and motor impairment. The patient reported an unspecified dysthyroidism discovered during the diagnostic work-up of AF, but no further investigations were performed. Bisoprolol, Edoxaban and Levodopa/Benserazide were started. In 2020 she had multiple hospitalization due to fall-related injuries, and multiple rib fractures. A neurological and cardiological reassessment did not highlight new problems, nor MSA-P progression, while discrepant thyroid function tests (TFTs) were found (TSH 2.4 mU/L, fT4 3.5 ng/dl, fT3 7.9 pg/ml; normal ranges: 0.4-4.5; 0.8-1.7 and 2.-5, respectively). Anterior pituitary function and a gadolinium-enhanced pituitary MRI were normal. Thyroid ultrasound revealed a modest goiter, with a normal vascularization and multiple hypo-anechoic and spongiform nodules ≤1 cm. Propylthiouracil has been started At referral in our Center, discrepant TFTs were confirmed (TSH 6.6 mU/L, fT4 2.5 ng/dL, fT3 5.1 pg/ml). TPOAb, TgAb and TRAb were absent. We also excluded assay interferences due to heterophiles antibodies. Being T3 administration contraindicated due to AF, a TRH-test, after suspension of PTU, was performed showing an intense and prolonged response of the TSH (36.7 and 19.2 mU/L at 30 and 120 minutes, respectively), consistent with RTHβ. Consistently, molecular analysis by a targeted NGS panel revealed a heterozygous known pathogenic variant in the exon 9 of the TRHB gene (c.1033G&amp;gt;A, p.Gly345Ser). Conclusion: In the differential diagnosis of central hyperthyroidism RTHβ should be considered even in older patients, as late diagnosis may occur. The association of RTHβ with MSA-P has never been reported before, although a causal relationship is improbable. Nevertheless, central hyperthyroidism could worsen underlying neurological diseases, given the critical role of TH in CNS and muscle. A greater awareness of both neurologists and endocrinologists on rare thyroid diseases is warranted, to improve the care of patients with neurological orphan diseases. Presentation: Friday, June 16, 2023

FRI476 Asymptomatic Thyrotropin-secreting Pituitary Microadenoma With Biochemical Secondary Hyperthyroidism: A Diagnostic Conundrum

Abstract Disclosure: G. Al-Naqeeb: None. R. Ghosh: None. P. Veeraraghavan: None. C. Cochran: None. J. Klubo-Gwiezdzinska: None. S. Gubbi: None. Background: Thyrotropin (TSH)-secreting pituitary adenomas (TSHAs) are often macroadenomas (&amp;gt;1 cm), and clinically present with secondary hyperthyroidism (SH), but clinically silent microTSHAs (&amp;lt;1 cm) with only biochemical SH pose a diagnostic challenge. Clinical Case: A 49-year-old, healthy male was referred to our center for evaluation of abnormal thyroid function tests (TFTs). Immunoassay (IA) measurements at an outside hospital had identified elevated free T4 (FT4), and an inappropriately normal TSH, and a pituitary magnetic resonance imaging (MRI) had noted an 8mm x 7mm non-invasive adenoma. The patient denied hyperthyroidism symptoms, medication/herbal supplement intake, radiation exposure, headaches, vision changes, and thyroid/pituitary disorders, or abnormal TFTs in relatives. Physical exam revealed no signs and symptoms of hyperthyroidism. No thyromegaly or cervical lymphadenopathy was felt. IA profile at our institute was consistent with an SH pattern [TSH: 3.32 mIU/L (NL: 0.4 - 4.7); FT4: 3 ng/dL (NL: 0.9 - 1.7); total T4: 14.5 mcg/dL (NL: 4.5 - 11.7); triiodothyronine: 266.6 ng/dL (NL: 80 - 200)], with similar values on repeat measurement. Equilibrium dialysis technique also yielded an elevated FT4 value. TSH-receptor, anti-thyroid peroxidase, and anti-thyroglobulin (Tg) antibody (Ab) titers, serum Tg, and thyroid binding globulin levels were normal. Dilution studies ruled out heterophile Ab interference. Familial dysalbuminemic hyperthyroxinemia was unlikely given the elevated FT4 values. Genetic testing revealed a normal THRB gene, thereby ruling out thyroid hormone resistance. THRA gene was not tested due to absence of behavioral or hearing issues. Markers of hyperthyroidism, including angiotensin converting enzyme, carotene, apolipoproteins, and osteocalcin levels were normal, except for an elevated sex hormone binding globulin of 104 nmol/L (NL: 11 - 78). Biochemical evaluation of other pituitary axes was normal. However, an elevated alpha sub-unit fraction (ASF) was noted on two separate measurements. Sonogram revealed a heterogeneous, hypervascular thyroid. Bone densitometry, echocardiogram, and Holter monitor studies were normal. The combination of biochemical SH, elevated ASF, pituitary adenoma, and exclusion of other etiologies causing SH pattern established the diagnosis of TSHA. An active surveillance approach was implemented. A pituitary MRI done 18 months later showed minimal (2mm in one axis) increase in the adenoma size, and the patient continued to demonstrate biochemical SH but remained asymptomatic. Conclusion: MicroTSHAs can present with asymptomatic SH. In this situation, excluding other biochemical SH etiologies is crucial to prevent unnecessary invasive procedures. But once TSHA diagnosis is established, due to the risk of tumor growth leading to symptomatic SH or mass effects, active surveillance is warranted. Presentation: Friday, June 16, 2023

TRβ Agonism Induces Tumor Suppression and Enhances Drug Efficacy in Anaplastic Thyroid Cancer in Female Mice.

Thyroid hormone receptor beta (TRβ) is a recognized tumor suppressor in numerous solid cancers. The molecular signaling of TRβ has been elucidated in several cancer types through re-expression models. Remarkably, the potential impact of selective activation of endogenous TRβ on tumor progression remains largely unexplored. We used cell-based and in vivo assays to evaluate the effects of the TRβ agonist sobetirome (GC-1) on a particularly aggressive and dedifferentiated cancer, anaplastic thyroid cancer (ATC). Here we report that GC-1 reduced the tumorigenic phenotype, decreased cancer stem-like cell populations, and induced redifferentiation of the ATC cell lines with different mutational backgrounds. Of note, this selective activation of TRβ amplified the effects of therapeutic agents in blunting the aggressive cell phenotype and stem cell growth. In xenograft assays, GC-1 alone inhibited tumor growth and was as effective as the kinase inhibitor, sorafenib. These results indicate that selective activation of TRβ not only induces a tumor suppression program de novo but enhances the effectiveness of anticancer agents, revealing potential novel combination therapies for ATC and other aggressive solid tumors.

Immunophenotyping of mice with mutated thyroid hormone receptor alpha or beta

Immunophenotyping of mice with mutated thyroid hormone receptor alpha or beta