Synthesis of thyroid hormone binding proteins transthyretin and albumin by human trophoblast

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Rafoxanide, a salicylanilide anthelmintic, interacts with human plasma protein transthyretin

Transthyretin (TTR) is a carrier protein for thyroid hormone thyroxine (T4 ) in plasma, placental cytosol, and cerebrospinal fluid. While the potential toxicity of small molecules that compete with T4 for binding to TTR should be carefully studied, these small molecules can also serve as anti-ATTR amyloidosis drugs by stabilizing the TTR structure. Here, we demonstrated that rafoxanide, an EU-approved anthelmintic drug for domesticated animals, binds to the T4 -binding site of TTR. An intrinsic fluorescence quenching assay showed that rafoxanide also binds to the thyroid hormone-related proteins, including serum albumin and thyroid hormone receptor β. Rafoxanide strongly inhibited TTR amyloidogenesis in fibrillization assay, but the binding of rafoxanide to TTR was interfered with in human plasma, probably due to interactions with thyroid hormone-related proteins. Protein crystallography provided clues for the optimization of binding affinity and selectivity. Our findings emphasize the importance of considering rafoxanide as both a possible thyroid-disrupting chemical and a lead compound for the development of new ATTR amyloidosis inhibitors.

Gestational Age-Dependent Regulation of Transthyretin in Mice during Pregnancy

Our prior studies have shown that protein misfolding and aggregation in the placenta are linked to the development of preeclampsia, a severe pregnancy complication. We identified transthyretin (TTR) as a key component of the aggregated protein complex. However, the regulation of native TTR in normal pregnancy remains unclear. In this study, we found that pregnant mice exhibited a remarkable and progressive decline in serum TTR levels through gestational day (gd) 12-14, followed by an increase in late pregnancy and postpartum. Meanwhile, serum albumin levels showed a modest but statistically significant increase throughout gestation. TTR protein and mRNA levels in the liver, a primary source of circulating TTR, mirrored the changes observed in serum TTR levels during gestation. Intriguingly, a similar pattern of TTR alteration was also observed in the serum of pregnant women and pregnant interleukin-10-knockout (IL-10-/-) mice with high inflammation background. In non-pregnant IL-10-/- mice, serum TTR levels were significantly lower than those in age-matched wild-type mice. Administration of IL-10 to non-pregnant IL-10-/- mice restored their serum TTR levels. Notably, dysregulation of TTR resulted in fewer implantation units, lower fetal weight, and smaller litter sizes in human TTR-overexpressing transgenic mice. Thus, TTR may play a pivotal role as a crucial regulator in normal pregnancy, and inflammation during pregnancy may contribute to the downregulation of serum TTR presence.

Transthyretin binds soluble endoglin and increases its uptake by hepatocytes: A possible role for transthyretin in preeclampsia?

BACKGROUND

Preeclampsia is a common but life-threatening condition of pregnancy. It is caused by poor placentation resulting in release of trophoblast material (including soluble endoglin (sEng)) into the maternal circulation leading to maternal vascular dysfunction and to the life-threatening condition of eclampsia. The only cure is early delivery, which can have lifelong consequences for the premature child. The thyroid hormone binding protein transthyretin is dysregulated in preeclampsia, however it is not known if this plays a role in disease pathology. We hypothesised that transthyretin may bind sEng and abrogate its negative effects by removing it from the maternal serum.

METHODS

The effect of transthyretin on hepatocyte uptake of Alexa-labelled sEng was measured using live cell imaging. Interactions between transthyretin, and sEng were investigated using molecular modelling, direct binding on CnBr Sepharose columns, confocal imaging, and measurement of fluorescence resonance energy transfer.

RESULTS

Transthyretin directly bound to sEng and increased its uptake by hepatocytes. This uptake was altered in the presence of transforming growth factor-β1 (TGF-β1). Molecular modelling predicted that transthyretin and TGF-β1 bind at the same site in sEng and may compete for binding. Endocytosed transthyretin and endoglin entered cells together and co-localised inside hepatocyte cells.

CONCLUSION

Transthyretin can bind sEng and increase its uptake from the extracellular medium. This suggests that increasing transthyretin levels or developing drugs that normalise or mimic transthyretin, may provide treatment options to reduce sEng induced vascular dysfunction.

Binding of common organic UV-filters to the thyroid hormone transport protein transthyretin using in vitro and in silico studies: Potential implications in health

Several anthropogenic contaminants have been identified as competing with the thyroid hormone thyroxine (T₄) for binding to transport proteins as transthyretin (TTR). This binding can potentially create toxicity mechanisms posing a threat to human health. Many organic UV filters (UVFs) and paraben preservatives (PBs), widely used in personal care products, are chemicals of emerging concern due to their adverse effects as potential thyroid-disrupting compounds. Recently, organic UVFs have been found in paired maternal and fetal samples and PBs have been detected in placenta, which opens the possibility of the involvement of TTR in the transfer of these chemicals across physiological barriers. We aimed to investigate a discrete set of organic UVFs and PBs to identify novel TTR binders. The binding affinities of target UVFs towards TTR were evaluated using in vitro T₄ competitive binding assays. The ligand-TTR affinities were determined by isothermal titration calorimetry (ITC) and compared with known TTR ligands. In parallel, computational studies were used to predict the 3-D structures of the binding modes of these chemicals to TTR. Some organic UVFs, compounds 2,2',4,4'-tetrahydroxybenzophenone (BP2, Kd = 0.43 μM); 2,4-dihydroxybenzophenone (BP1, Kd = 0.60 μM); 4,4'-dihydroxybenzophenone (4DHB, Kd = 0.83 μM), and 4-hydroxybenzophenone (4HB, Kd = 0.93 μM), were found to display a high affinity to TTR, being BP2 the strongest TTR binder (ΔH = -14.93 Kcal/mol). Finally, a correlation was found between the experimental ITC data and the TTR-ligand docking scores obtained by computational studies. The approach integrating in vitro assays and in silico methods constituted a useful tool to find TTR binders among common organic UVFs. Further studies on the involvement of the transporter protein TTR in assisting the transplacental transfer of these chemicals across physiological barriers and the long-term consequences of prenatal exposure to them should be pursued.

Thyroid hormones: Metabolism and transportation in the fetoplacental unit

The thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3), are of vital importance for fetal development. The concentration of THs in fetal circulation varies throughout gestation and differs from the concentration in the maternal serum, indicating the presence of maternal-fetal thyroid homeostasis regulatory mechanisms in the placenta. The passage of THs from maternal circulation to fetal circulation is modulated by plasma membrane transporters, enzymes, and carrier proteins. Monocarboxylate transporter 8, iodothyronine deiodinases (DIO2 and DIO3), and transthyretin are especially involved in this maternal-fetal thyroid modulation, shown by a greater expression in the placenta. THs also play a role in placental development and as expected, abnormal variations in TH levels are associated with pregnancy complications and can result in damage to the fetus. Although new evidence regarding TH regulation during pregnancy and its effects in the mother, placenta, and fetus has been published, many aspects of these interactions are still poorly understood. The objective of this review is to provide an evidence-based update, drawn from current data, on the metabolism and transport of THs in the placenta and their vital role in the maternal-fetal relationship.

The Journey of Human Transthyretin: Synthesis, Structure Stability, and Catabolism

Transthyretin (TTR) is a homotetrameric protein mainly synthesised by the liver and the choroid plexus whose function is to carry the thyroid hormone thyroxine and the retinol-binding protein bound to retinol in plasma and cerebrospinal fluid. When the stability of the tetrameric structure is lost, it breaks down, paving the way for the aggregation of TTR monomers into insoluble fibrils leading to transthyretin (ATTR) amyloidosis, a progressive disorder mainly affecting the heart and nervous system. Several TTR gene mutations have been characterised as destabilisers of TTR structure and are associated with hereditary forms of ATTR amyloidosis. The reason why also the wild-type TTR is intrinsically amyloidogenic in some subjects is largely unknown. The aim of the review is to give an overview of the TTR biological life cycle which is largely unknown. For this purpose, the current knowledge on TTR physiological metabolism, from its synthesis to its catabolism, is described. Furthermore, a large section of the review is dedicated to examining in depth the role of mutations and physiological ligands on the stability of TTR tetramers.

Evidence From Human Placenta, Endoplasmic Reticulum-Stressed Trophoblasts, and Transgenic Mice Links Transthyretin Proteinopathy to Preeclampsia

BACKGROUND

We have demonstrated that protein aggregation plays a pivotal role in the pathophysiology of preeclampsia and identified several aggregated proteins in the circulation of preeclampsia patients, the most prominent of which is the serum protein TTR (transthyretin). However, the mechanisms that underlie protein aggregation remain poorly addressed.

METHODS

We examined TTR aggregates in hypoxia/reoxygenation-exposed primary human trophoblasts (PHTs) and the preeclampsia placenta using complementary approaches, including a novel protein aggregate detection assay. Mechanistic analysis was performed in hypoxia/reoxygenation-exposed PHTs and Ttr transgenic mice overexpressing transgene-encoded wild-type human TTR or Ttr^-/- mice. High-resolution ultrasound analysis was used to measure placental blood flow in pregnant mice.

RESULTS

TTR aggregation was inducible in PHTs and the TCL-1 trophoblast cell line by endoplasmic reticulum stress inducers or autophagy-lysosomal disruptors. PHTs exposed to hypoxia/reoxygenation showed increased intracellular BiP (binding immunoglobulin protein), phosphorylated IRE1α (inositol-requiring enzyme-1α), PDI (protein disulfide isomerase), and Ero-1, all markers of the unfolded protein response, and the apoptosis mediator caspase-3. Blockade of IRE1α inhibited hypoxia/reoxygenation-induced upregulation of Ero-1 in PHTs. Excessive unfolded protein response activation was observed in the early-onset preeclampsia placenta. Importantly, pregnant human TTR mice displayed aggregated TTR in the junctional zone of the placenta and severe preeclampsia-like features. High-resolution ultrasound analysis revealed low blood flow in uterine and umbilical arteries in human TTR mice compared with control mice. However, Ttr^-/- mice did not show any pregnancy-associated abnormalities.

CONCLUSIONS

These observations in the preeclampsia placenta, cultured trophoblasts, and Ttr transgenic mice indicate that TTR aggregation is an important causal contributor to preeclampsia pathophysiology.

Nicotine binds to the transthyretin-thyroxine complex and reduces its uptake by placental trophoblasts

BACKGROUND

A supply of maternal thyroid hormone (thyroxine, T4) is essential for normal human fetal development. Human placental trophoblasts synthesize, secrete and take up the T4 binding protein transthyretin, providing a route for maternal T4 to enter the placenta. Transthyretin is also involved in T4 transport in other tissues such as the brain choroid plexus. Nicotine alters transthyretin synthesis and function in rat choroid plexus. If nicotine influences trophoblast turnover of transthyretin, then it may directly affect placental transfer of T4 to the developing fetus and contribute to the negative impacts of smoking on fetal growth, development and placental function.

METHODS

The effect of nicotine on trophoblast uptake of Alexa-labelled transthyretin was measured using live cell imaging. The effect of nicotine on protein expression was measured by western blotting. Interactions between transthyretin, T4 and nicotine were investigated using chemical cross-linking techniques and molecular dynamic simulations.

RESULTS

Nicotine blocks uptake of transthyretin-T4 by human placental trophoblast cells. Nicotine reduces the expression of the trophoblast scavenger receptor class B type 1 (SR-B1) that plays a role in transthyretin-T4 uptake. Molecular dynamic modelling suggests that when T4 is bound to transthyretin, nicotine binding increases tetramer stability, reducing the ability of the transthyretin-T4 complex to enter trophoblast cells.

CONCLUSION

Our data suggest that nicotine exposure during pregnancy reduces transplacental transport of transthyretin and T4 to the placenta and developing fetus. This may contribute to the negative effects of smoking on fetal growth, development and pregnancy viability.

Impact of endocrine disrupting chemicals on neurodevelopment: the need for better testing strategies for endocrine disruption-induced developmental neurotoxicity

INTRODUCTION

Brain development is highly dependent on hormonal regulation. Exposure to chemicals disrupting endocrine signaling has been associated with neurodevelopmental impairment. This raises concern about exposure to the suspected thousands of endocrine disruptors, and has resulted in efforts to improve regulation of these chemicals. Yet, the causal links between endocrine disruption and developmental neurotoxicity, which would be required for regulatory action, are still largely missing.

AREAS COVERED

In this review, we illustrate the importance of two endocrine systems, thyroid hormone and retinoic acid pathways, for neurodevelopment. We place special emphasis on TH and RA synthesis, metabolism, and how endocrine disrupting chemicals known or suspected to affect these systems are associated with developmental neurotoxicity.

EXPERT OPINION

While it is clear that neurodevelopment is dependent on proper hormonal functioning, and evidence is increasing for developmental neurotoxicity induced by endocrine disrupting chemicals, this is not grasped by current chemical testing. Thus, there is an urgent need to develop test methods detecting endocrine disruption in the context of neurodevelopment. Key to this development is further mechanistic insights on the involvement of endocrine signaling in neurodevelopment as well as increased support to develop and validate new test methods for the regulatory context.

Gaps in the knowledge of thyroid hormones and placental biology

Thyroid hormones (THs) are required for the growth and development of the foetus, stimulating anabolism and oxygen consumption from the early stages of pregnancy to the period of foetal differentiation close to delivery. Maternal changes in the hypothalamic–pituitary thyroid axis are also well known. In contrast, several open questions remain regarding the relationships between the placenta and the maternal and foetal TH systems. The exact mechanism by which the placenta participates in regulating the TH concentration in the foetus and mother and the role of TH in the placenta are still poorly studied. In this review, we aim to summarize the available data in the area and highlight significant gaps in our understanding of the ontogeny and cell-specific localization of TH transporters, TH receptors and TH metabolic enzymes in the placenta in both human and rodent models. Significant deficiencies also exist in knowledge of the contribution of genomic and nongenomic effects of TH on the placenta and finally how the placenta reacts during pregnancy when the mother has thyroid disease. By addressing these key knowledge gaps, improved pregnancy outcomes and management of women with thyroid alterations may be possible.

Physiological and metabolic adaptations in pregnancy: importance of trimester-specific reference intervals to investigate maternal health and complications

Diagnosis, prognostication, and monitoring of maternal health throughout pregnancy relies on laboratory testing, including but not limited to key markers of thyroid, hepatic, cardiac, hematology, and renal function. Dynamic physiological processes during gestation significantly influence the maternal biochemistry that supports both the mother and fetus. Resultant changes in blood biochemistry alter the expected values of common laboratory tests. However, the importance of pregnancy-specific reference intervals for laboratory test result interpretation and appropriate monitoring of maternal health and complications is underappreciated. Most clinical laboratories continue to use non-pregnant adult reference intervals for laboratory test interpretation in pregnancy. The current review summarizes and critically evaluates the available literature regarding physiological and metabolic adaptations in pregnancy and their influence on common biomarkers of health and disease. The main laboratory parameters discussed include thyroid, hepatic, metabolic, renal, hematology, inflammatory, and cardiac markers. Considering the available data, further studies are urgently needed to establish trimester-specific reference intervals in healthy pregnant women on updated analytical platforms. Without such data, the standard of clinical laboratory service in pregnancy remains compromised and affects the quality of maternal-fetal healthcare.

The role of transthyretin in cell biology: impact on human pathophysiology

Transthyretin (TTR) is an extracellular protein mainly produced in the liver and choroid plexus, with a well-stablished role in the transport of thyroxin and retinol throughout the body and brain. TTR is prone to aggregation, as both wild-type and mutated forms of the protein can lead to the accumulation of amyloid deposits, resulting in a disease called TTR amyloidosis. Recently, novel activities for TTR in cell biology have emerged, ranging from neuronal health preservation in both central and peripheral nervous systems, to cellular fate determination, regulation of proliferation and metabolism. Here, we review the novel literature regarding TTR new cellular effects. We pinpoint TTR as major player on brain health and nerve biology, activities that might impact on nervous systems pathologies, and assign a new link between TTR and angiogenesis and cancer. We also explore the molecular mechanisms underlying TTR activities at the cellular level, and suggest that these might go beyond its most acknowledged carrier functions and include interaction with receptors and activation of intracellular signaling pathways.

RNA-Seq reveals changes in human placental metabolism, transport and endocrinology across the first-second trimester transition

The human placenta is exposed to major environmental changes towards the end of the first trimester associated with full onset of the maternal arterial placental circulation. Changes include a switch from histotrophic to hemotrophic nutrition, and a threefold rise in the intraplacental oxygen concentration. We evaluated their impact on trophoblast development and function using RNA-sequencing (RNA-Seq) and DNA-methylation analyses performed on the same chorionic villous samples at 7-8 (n=8) and 13-14 (n=6) weeks of gestation. Reads were adjusted for fetal sex. Most DEGs were associated with protein processing in the endoplasmic reticulum (ER), hormone secretion, transport, extracellular matrix, vasculogenesis, and reactive oxygen species metabolism. Transcripts higher in the first trimester were associated with synthesis and ER processing of peptide hormones, and glycolytic pathways. Transcripts encoding proteins mediating transport of oxygen, lipids, protein, glucose, and ions were significantly increased in the second trimester. The motifs of CBX3 and BCL6 were significantly overrepresented, indicating the involvement of these transcription factor networks in the regulation of trophoblast migration, proliferation and fusion. These findings are consistent with a high level of cell proliferation and hormone secretion by the early placenta to secure implantation in a physiological low-oxygen environment.

Evolution of thyroid hormone distributor proteins in fish

In plasma, thyroid hormone (TH) is bound to several TH distributor proteins (THDPs), constituting a TH delivery/distribution network. Extensive studies of THDPs from tetrapods has proposed an evolutionary scenario concerning structural and functional changes in THDPs, especially for transthyretin (TTR). When assessing, in an evolutionary context, the roles of THDPs as a component constituting part of the vertebrate thyroid system, the data from fish THDPs are critical. In this review the phylogenetic distributions, spatiotemporal expression patterns and binding properties of THDPs in fish are described, and the question of whether the evolutionary hypotheses proposed in tetrapod THDPs can be applied to fish THDPs is assessed. The phylogenetic distributions of THDPs are highly variable among fish groups. Analysis in this review reveals that the evolutionary hypotheses proposed in tetrapod THDPs cannot be applied to fish THDPs, and that the role of plasma lipoproteins as THDPs grows in importance in fish groups. In primitive fish, zinc is an import factor in TH binding to TTR, and high zinc content may facilitate the acquisition of high TH binding activity during the early evolution of TTR. Finally, the possible roles of THDPs in the vertebrate thyroid system are discussed.

Physiological Role and Use of Thyroid Hormone Metabolites - Potential Utility in COVID-19 Patients

Thyroxine and triiodothyronine (T3) are classical thyroid hormones and with relatively well-understood actions. In contrast, the physiological role of thyroid hormone metabolites, also circulating in the blood, is less well characterized. These molecules, namely, reverse triiodothyronine, 3,5-diiodothyronine, 3-iodothyronamine, tetraiodoacetic acid and triiodoacetic acid, mediate both agonistic (thyromimetic) and antagonistic actions additional to the effects of the classical thyroid hormones. Here, we provide an overview of the main factors influencing thyroid hormone action, and then go on to describe the main effects of the metabolites and their potential use in medicine. One section addresses thyroid hormone levels in corona virus disease 19 (COVID-19). It appears that i) the more potently-acting molecules T3 and triiodoacetic acid have shorter half-lives than the less potent antagonists 3-iodothyronamine and tetraiodoacetic acid; ii) reverse T3 and 3,5-diiodothyronine may serve as indicators for metabolic dysregulation and disease, and iii) Nanotetrac may be a promising candidate for treating cancer, and resmetirom and VK2809 for steatohepatitis. Further, the use of L-T3 in the treatment of severely ill COVID-19 patients is critically discussed.

Mother to Fetus Transfer of Hydroxylated Polychlorinated Biphenyl Congeners (OH-PCBs) in the Japanese Macaque (Macaca fuscata): Extrapolation of Exposure Scenarios to Humans

Prenatal hydroxylated polychlorinated biphenyls (OH-PCBs) exposure may disrupt fetal brain development during the critical period of thyroid hormone (TH) action. However, there are limited studies on the OH-PCB transfer to the fetal brain, particularly in primates. In this study, we selected the Japanese macaque (Macaca fuscata) as a model animal for the fetal transfer of OH-PCBs in humans and revealed OH-PCB concentrations and their relationships in maternal and fetal blood, liver, and brain. l-thyroxine (T4)-like OH-PCBs including 4OH-CB187, a major congener in humans, were found in high proportions in the blood, liver, brain, and placenta of pregnant Japanese macaques. OH-PCBs were detected in the fetal brain and liver in the first trimester, indicating their transfer to the brain in the early pregnancy stage. 4OH-CB187 and 4OH-CB202 were the major congeners found in fetal brain, indicating that these T4-like OH-PCBs are transported from maternal blood to the fetal brain via the placenta. These results indicate that further studies are needed on the effects of OH-PCBs on the developing fetal brain.

MFGE8, ALB, APOB, APOE, SAA1, A2M, and C3 as Novel Biomarkers for Stress Cardiomyopathy

BACKGROUND

Stress cardiomyopathy (SCM) is a transient reversible left ventricular dysfunction that more often occurs in women. Symptoms of SCM patients are similar to those of acute coronary syndrome (ACS), but little is known about biomarkers. The goals of this study were to identify the potentially crucial genes and pathways associated with SCM.

METHODS

We analyzed microarray datasets GSE95368 derived from the Gene Expression Omnibus (GEO) database. Firstly, identify the differentially expressed genes (DEGs) between SCM patients in normal patients. Then, the DEGs were used for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Finally, the protein-protein interaction (PPI) network was constructed and Cytoscape was used to find the key genes.

RESULTS

In total, 25 DEGs were identified, including 10 upregulated genes and 15 downregulated genes. These DEGs were mainly enriched in ECM-receptor interaction, dilated cardiomyopathy (DCM), human papillomavirus infection, and focal adhesion, whereas in GO function classification, they were mainly enriched in the extracellular region, positive regulation of the multicellular organismal process, establishment of localization, and intracellular vesicle.

CONCLUSION

Seven hub genes contained APOE, MFGE8, ALB, APOB, SAA1, A2M, and C3 identified as hub genes of SCM, which might be used as diagnostic biomarkers or molecular targets for the treatment of SCM.

Association between transthyretin concentrations and gestational diabetes mellitus in Chinese women

BACKGROUND

Transthyretin (TTR) is considered to be associated with insulin resistance in humans. This study aimed to investigate TTR level in gestational diabetes mellitus (GDM) and its association with glucose metabolism.

METHODS

Fifty pregnant women with GDM and 47 pregnant women with normal glucose tolerance matched for body mass index and age were enrolled in this study. Their blood samples were collected to detect TTR, retinol-binding protein 4 (RBP4), and their association with glucose and lipid metabolism.

RESULTS

Serum TTR levels in the GDM group were significantly higher than those in the control group (median, 93.44 [interquartile range, 73.81, 117.79] μg/ml vs. 80.83 [74.19, 89.38] μg/ml; P = 0.006). GDM subjects had a lower RBP4/TTR ratio than the control subjects (median, 517.57 [interquartile range, 348.38, 685.27] vs. 602.56 [460.28, 730.62]; P = 0.02). The serum TTR concentrations were positively associated with neonatal weight (r = 0.223, P = 0.028), homeostatic model assessment of insulin resistance (r = 0.246, P = 0.015), and fasting blood glucose (FBG) (r = 0.363, P < 0.001). In stepwise multivariate linear regression analysis, FBG (standardized beta = 0.27, P = 0.004) and neonatal weight (standardized beta = 0.345, P < 0.001) were independent predictors of serum TTR concentrations. Additionally, FBG (standardized beta = - 0.306, P = 0.002) and triglyceride (TG) (beta = 0.219, P = 0.025) were independently associated with RBP4/TTR ratio.

CONCLUSIONS

Serum TTR concentrations were significantly higher in women with GDM than that in women without GDM, suggesting that elevated TTR level may play a role in the pathogenesis of GDM. Meanwhile, TTR was positively and independently associated with FBG and neonatal weight, while FBG and TG were independent predictors of RBP4/TTR ratio. Moreover, serum TTR levels and RBP4/TTR ratio were considered valuable markers of insulin resistance and GDM.

Evaluation of structurally different brominated flame retardants interacting with the transthyretin and their toxicity on HepG2 cells

Brominated flame retardants (BFRs) are found at quantifiable levels in both humans and wildlife and may potentially cause a health risk. For BFRs and their derivatives, limited information regarding the relationship among the structure, binding affinity to the target protein and toxicity is currently available. In the present work, representative BFRs with different hydroxyl- or bromo-substituents, namely 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47), 3-hydroxy-2, 2', 4, 4'-tetrabromodiphenyl ether (3-OH-BDE-47) and tetrabromobisphenol A (TBBPA), were selected to investigate the interactions with transthyretin (TTR) by electrospray ionization mass spectrometry (ESI-MS) and cytotoxicity on HepG2 cells. It was noted that BDE-47 had a weak binding affinity to TTR, while 3-OH-BDE-47 and TBBPA had a stronger binding affinity than BDE-47 and thyroxine (T4). Hence, 3-OH-BDE-47 and TBBPA could affect the binding of TTR with its native ligand T₄ by competitive binding to TTR, even at equal concentrations, which might be associated with BFR toxicity of endocrine disruption. Negative cooperativity was found for 3-OH-BDE-47 and TBBPA binding to TTR, similar to T₄ with a well-established negatively cooperative binding mechanism. The tendency of toxic effects on HepG2 cells for these three BFRs was, 3-OH-BDE-47 > TBBPA > BDE-47, and this order was in good agreement with the binding ability explored by ESI-MS experiments and molecular docking simulation. The observations obtained by this study demonstrate that the binding properties of these BFRs to TTR and their cytotoxicity are correlated with structure differentials and functional substituents.

Divergence of Iodine and Thyroid Hormones in the Fetal and Maternal Parts of Human-Term Placenta

The human placenta is an important organ that forms a barrier where maternal and fetal exchange takes place. The placenta transport iodine to the fetal circulation by transfer of maternal iodine and deiodination of thyroid hormones (THs). The aim of the study was to examine the distribution of iodine and thyroid hormone transporters in the maternal and fetal sides of human-term placenta. A cross-sectional study was performed at the First Affiliated Hospital of China Medical University. Placental samples (maternal and fetal surfaces) were collected from 113 healthy-term pregnant women. The iodine content; the concentration of thyroxine (T4), triiodothyronine (T3), and reverse T3 (rT3); and the enzyme activity of placental type 2 iodothyronine deiodinase (D2) and D3 were examined. The mRNA and protein localization/expression of iodine and thyroid hormone transporters in the placenta were also studied. We also analyzed the association between expression level of Na+/I- symporter (NIS), thyroid hormone transporter protein, D3 activity in maternal and fetal surfaces of placenta with iodine content, and thyroid hormone levels. Iodine levels in placental samples from the maternal side were significantly higher than those in samples from the fetal side. T3 and T4 expression in fetal placenta was significantly lower than in maternal placenta. D3 activity in the fetal side of the placentas was significantly higher than that in the maternal side. The mRNA and protein expression of monocarboxylate transporters 8 (MCT8), L-amino acid transporters 1 (LAT1), organic anion transporting polypeptides 4A1 (OATP4A1), and TH binding protein transthyretin (TTR) were significantly increased in maternal side, while the NIS expression was higher in fetal side of human-term placenta. In conclusion, the enzymatic deiodination of thyroid hormones forms a barrier which reduces transplacental passage of the hormones and that the maternal part of the placenta is the primary factor in the mechanism regulating the hormonal transfer.

Transport of maternal transthyretin to the fetus in the viviparous teleost Neoditrema ransonnetii (Perciformes, Embiotocidae)

The molecular basis of viviparity in non-mammalian species has not been widely studied. Neoditrema ransonnetii, a surfperch, is a matrotrophic teleost whose fetuses grow by ovarian cavity fluid (OCF) ingestion and by nutrient absorption via their enlarged hindgut. We performed a proteomics analysis of N. ransonnetii plasma protein and found proteins specific to pregnant females; one of these was identified as transthyretin (TTR), a thyroid hormone distributor protein. We synthesized recombinant protein rNrTTR and raised an antibody, anti-rNrTTR, against it. Semi-quantitative analysis by western blotting using the antibody demonstrated that plasma TTR levels were significantly greater in pregnant fish than in non-pregnant fish. OCF and fetal plasma also contained high TTR levels. Immunohistochemical staining showed that large amounts of maternal TTR were taken up by fetal intestinal epithelial cells. These results indicate that maternal TTR is secreted into OCF and taken up by fetal enterocytes, presumably to deliver thyroid hormones to developing fetuses.

Transthyretin Maintains Muscle Homeostasis Through the Novel Shuttle Pathway of Thyroid Hormones During Myoblast Differentiation

Skeletal muscle, the largest part of the total body mass, influences energy and protein metabolism as well as maintaining homeostasis. Herein, we demonstrate that during murine muscle satellite cell and myoblast differentiation, transthyretin (TTR) can exocytose via exosomes and enter cells as TTR- thyroxine (T₄) complex, which consecutively induces the intracellular triiodothyronine (T₃) level, followed by T₃ secretion out of the cell through the exosomes. The decrease in T₃ with the TTR level in 26-week-old mouse muscle, compared to that in 16-week-old muscle, suggests an association of TTR with old muscle. Subsequent studies, including microarray analysis, demonstrated that T₃-regulated genes, such as FNDC5 (Fibronectin type III domain containing 5, irisin) and RXRγ (Retinoid X receptor gamma), are influenced by TTR knockdown, implying that thyroid hormones and TTR coordinate with each other with respect to muscle growth and development. These results suggest that, in addition to utilizing T₄, skeletal muscle also distributes generated T₃ to other tissues and has a vital role in sensing the intracellular T₄ level. Furthermore, the results of TTR function with T₄ in differentiation will be highly useful in the strategic development of novel therapeutics related to muscle homeostasis and regeneration.

MicroRNA regulation of transthyretin in trophoblast biofunction and preeclampsia

Preeclampsia (PE) is the major cause of maternal, fetal and neonatal mortality affecting approximately 2-7% of pregnancies. Transthyretin (TTR) is down-regulated in PE pregnancies serum and placenta. Our bioinformatic analysis showed that TTR is a predicted target for miR-200a-3p and miR-141-3p. The aim of this study was to determine whether miR-200a-3p and miR-141-3p are involved in preeclampsia through its targeting of TTR in human placental trophoblasts. In human PE placenta, TTR transcript and protein levels were significantly lower associated with high expression of miR-141-3p and 200a-3p. We found that miR-200a-3p and miR-141-3p inhibited TTR expression by directly binding to the 3'UTR of TTR, which is reversed by mutation in the microRNA binding site. In preeclamptic plasm, TTR levels were significantly downregulated. TTR was validated as a direct target of miR-200a-3p and miR-141-3p using dual luciferase assays in JEG3 cells. Transwell insert invasion assays showed that TTR mediated the invasion-inhibitory effect of miR-200a-3p and miR-141-3p in JEG3 cells. These data provides new insight into physiological role of miR-141-3p and miR-200a-3p in regulating TTR during trophoblast dysfunction and PE development.

Thyroid hormones and female reproduction

Thyroid hormones are vital for the proper functioning of the female reproductive system, since they modulate the metabolism and development of ovarian, uterine, and placental tissues. Therefore, hypo- and hyperthyroidism may result in subfertility or infertility in both women and animals. Other well-documented sequelae of maternal thyroid dysfunctions include menstrual/estral irregularity, anovulation, abortion, preterm delivery, preeclampsia, intrauterine growth restriction, postpartum thyroiditis, and mental retardation in children. Several studies have been carried out involving prospective and retrospective studies of women with thyroid dysfunction, as well as in vivo and in vitro assays of hypo- and hyperthyroidism using experimental animal models and/or ovarian, uterine, and placental cell culture. These studies have sought to elucidate the mechanisms by which thyroid hormones influence reproduction to better understand the physiology of the reproductive system and to provide better therapeutic tools for reproductive dysfunctions that originate from thyroid dysfunctions. Therefore, this review aims to summarize and update the available information related to the role of thyroid hormones in the morphophysiology of the ovary, uterus, and placenta in women and animals and the effects of hypo- and hyperthyroidism on the female reproductive system.

Maternal exposures to persistent organic pollutants are associated with DNA methylation of thyroid hormone-related genes in placenta differently by infant sex

Exposure to persistent organic pollutants (POPs) during pregnancy is associated with a disruption in thyroid hormone balance. The placenta serves as an important environment for fetal development and also regulates thyroid hormone supply to the fetus. However, epigenetic changes of thyroid regulating genes in placenta have rarely been studied. This study was conducted to evaluate the association between several POP concentrations in maternal serum and DNA methylation of thyroid hormone-related genes in the placenta. The placenta samples were collected from 106 Korean mother at delivery, and the promoter methylation of the placental genes was measured by a bisulfite pyrosequencing. The deiodinase type 3 (DIO3), monocarboxylate transporter 8 (MCT8), and transthyretin (TTR) genes were selected as the target genes as they play an important role in the regulation of fetal thyroid balance. Because people are exposed to multiple chemicals at the same time, a multiple-POP model using principal component analysis (PCA) was applied to evaluate the association between the multiple POPs exposure and the epigenetic change in placenta. In addition, a single-POP model which includes one chemical each in the statistical model for association was conducted. Based on the single-POP models, serum concentrations of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and brominated diphenyl ether-47 (BDE-47) were significantly associated with an increase in placental DIO3 methylation, but only among female infants. Among male infants, a positive association between serum p,p'-DDT and MCT8 methylation level was found. According to the multiple-POP models, serum DDTs were positively associated with DIO3 methylation in the placenta of female infants, while a positive association with MCT8 methylation was observed in those of the male infants. Our observation showed that in utero exposure to DDTs may influence the DNA methylation of DIO3 and MCT8 genes in the placenta, in a sexually dimorphic manner. These alterations in placental epigenetic regulation may in part explain the thyroid hormone disruption observed among the newborns or infants followed by in utero exposure to POPs.

Limited Chemical Structural Diversity Found to Modulate Thyroid Hormone Receptor in the Tox21 Chemical Library

BACKGROUND

Thyroid hormone receptors (TRs) are critical endocrine receptors that regulate a multitude of processes in adult and developing organisms, and thyroid hormone disruption is of high concern for neurodevelopmental and reproductive toxicities in particular. To date, only a small number of chemical classes have been identified as possible TR modulators, and the receptors appear highly selective with respect to the ligand structural diversity. Thus, the question of whether TRs are an important screening target for protection of human and wildlife health remains.

OBJECTIVE

Our goal was to evaluate the hypothesis that there is limited structural diversity among environmentally relevant chemicals capable of modulating TR activity via the collaborative interagency Tox21 project.

METHODS

We screened the Tox21 chemical library (8,305 unique structures) in a quantitative high-throughput, cell-based reporter gene assay for TR agonist or antagonist activity. Active compounds were further characterized using additional orthogonal assays, including mammalian one-hybrid assays, coactivator recruitment assays, and a high-throughput, fluorescent imaging, nuclear receptor translocation assay.

RESULTS

Known agonist reference chemicals were readily identified in the TR transactivation assay, but only a single novel, direct agonist was found, the pharmaceutical betamipron. Indirect activation of TR through activation of its heterodimer partner, the retinoid-X-receptor (RXR), was also readily detected by confirmation in an RXR agonist assay. Identifying antagonists with high confidence was a challenge with the presence of significant confounding cytotoxicity and other, non-TR-specific mechanisms common to the transactivation assays. Only three pharmaceuticals-mefenamic acid, diclazuril, and risarestat-were confirmed as antagonists.

DISCUSSION

The results support limited structural diversity for direct ligand effects on TR and imply that other potential target sites in the thyroid hormone axis should be a greater priority for bioactivity screening for thyroid axis disruptors. https://doi.org/10.1289/EHP5314.

Scavenger Receptor Class B Member 1 Independent Uptake of Transthyretin by Cultured Hepatocytes Is Regulated by High Density Lipoprotein

Thyroid hormone (thyroxine, T4) is essential for the normal function of all cell types and is carried in serum bound to several proteins including transthyretin. Recently, evidence has emerged of alternate pathways for hormone entry into cells that are dependent on hormone binding proteins. Transthyretin and transthyretin bound T4 are endocytosed by placental trophoblasts through the high-density lipoprotein receptor, Scavenger Receptor Class B Type 1 (SR-B1). High density lipoprotein (HDL) affects the expression and function of SR-B1 in trophoblast cells. SR-B1 is also expressed in hepatocytes and we sought to determine if hepatocyte SR-B1 was involved in transthyretin or transthyretin-T4 uptake and whether uptake was affected by HDL. Transthyretin and transthyretin-T4 uptake by hepatocytes is not dependent on SR-B1. HDL treatment reduced SR-B1 expression. However, pretreatment of hepatocytes with HDL increased uptake of transthyretin-T4. Knockdown of SR-B1 expression using siRNA also increased transthyretin-T4 uptake. Coaddition of HDL to transthyretin uptake experiments blocked both transthyretin and transthyretin-T4 uptake. Hepatocyte uptake of transthyretin-T4 uptake is influenced by, but is not dependent on, SR-B1 expression. HDL also decreases transthyretin-T4 uptake and therefore diet or drugs may interfere with this process. This suggests that multiple lipoprotein receptors may be involved in the regulation of uptake of transthyretin-T4 in a cell-type specific manner. Further study is required to understand this important process.

Review shows that thyroid hormone substitution could benefit transient hypothyroxinaemia of prematurity but treatment strategies need to be clarified

AIM

Thyroid hormones are crucial for foetal and neonatal brain development. This paper provides an overview of the normal role of thyroid hormones in foetal brain development and the pathophysiology of transient hypothyroxinaemia of prematurity (THOP). It also discusses the diagnostic and therapeutic controversies around THOP and looks at directions for future research.

METHODS

We used the PubMed and Embase databases to identify papers published in English from 1969 to June 2018. This identified 20 papers about the impact of THOP on neurodevelopment and seven randomised controlled trials about therapeutic approaches from 1981-2016.

RESULTS

THOP has been researched for more than three decades. The impact of temporarily low thyroxine levels, without any increase in pituitary-secreted thyroid-stimulating hormone at a critical timeframe in an infant's brain development, is still debated. Heterogeneity in THOP definitions, difficulties with thyroid hormone assessment, identifying patients at risk and a clear lack of sufficiently powered studies add to the current controversy. There are indications that thyroid hormone substitution might be useful in extremely low gestational age neonates with THOP.

CONCLUSION

Some preterm infants could benefit from THOP treatment, but more studies are needed to clarify further treatment strategies, including the optimal timing of initiation and duration.

The placenta in fetal thyroid hormone delivery: from normal physiology to adaptive mechanisms in complicated pregnancies

Context: Thyroid hormones are indispensable for normal fetal development. Since the fetus depends to a large extent on maternal thyroid hormone supply through the placenta, this challenges maternal thyroid economy. Several molecular mechanisms are involved in placental thyroid hormone transport and metabolism. Chronic pregnancy complications, associated with utero-placental hypoxia, trigger the development of accelerated placental maturation in order to improve fetal-placental exchange to strengthen the offspring's chance of survival. This review provides an overview of normal maternal-fetal thyroid hormone supply and explores the presence of placental adaptive mechanisms in complicated pregnancies with chronical utero-placental hypoxia to improve the thyroid hormone supply to the fetus under pressure, to end with reflections about the long term health consequences.Evidence acquisition: This work is based on a comprehensive literature review of the PubMed and Embase database, including relevant articles from 1969 to June 2018.Conclusions: The placenta is actively involved in fetal thyroid hormone delivery through a combination of stimulatory and inhibitory mechanisms. Parallel with histological adaptations to improve transplacental fetal-maternal exchange, there are indications of placental adaptive mechanisms in thyroid hormone transport and metabolism in case of complicated pregnancies, from animal models and in-vitro experiments. Evidence from human in-vivo studies is limited due to heterogeneity in study populations, small study samples, and technical limitations. Further research is necessary to reveal the role of the placenta in pathological circumstances. The placenta might thus be considered as the infants' black box of pregnancy. Results will contribute to more insights in the concept of fetal programming, which lays the foundations of optimum health, growth, and neurodevelopment across the lifespan.

Transthyretin uptake in placental cells is regulated by the high-density lipoprotein receptor, scavenger receptor class B member 1

Transfer of thyroid hormone into cells is critical for normal physiology and transplacental transfer of maternal thyroid hormones is essential for normal fetal growth and development. Free thyroid hormone is known to enter cells through specific cell surface transport proteins, and for many years this uptake of unbound thyroid hormones was assumed to be the only relevant mechanism. Recently, evidence has emerged of alternate pathways for hormone entry into cells that are dependent on hormone binding proteins. In this study we identify the high-density lipoprotein receptor Scavenger Receptor class B member 1 (SR-B1) as important in the uptake and transport of transthyretin-bound thyroid hormone by placental trophoblast cells. High-density lipoprotein increases expression of SR-B1 in placental cells but also reduces uptake of transthyretin-thyroid hormone through the SR-B1 transporter. SR-B1 is expressed in many cells and this study suggests that SR-B1 may be universally important in thyroid hormone uptake. Further investigation of SR-B1-TTR interactions may fundamentally change our understanding of hormone biology and have important clinical consequences.

Diflunisal tolerability in transthyretin cardiac amyloidosis: a single center's experience

OBJECTIVE

Transthyretin (ATTR) amyloidosis is an under-recognized, progressive disease manifesting as cardiomyopathy and/or polyneuropathy. Diflunisal, a nonsteroidal anti-inflammatory drug (NSAID), has demonstrated transthyretin stabilization in vitro and slowing of polyneuropathy progression in the hereditary ATTR subtype (ATTRm). However, the use of diflunisal has only been described in a small cohort of patients with ATTR cardiac amyloidosis (CA). We hypothesized that selected patients with ATTR-CA, both hereditary and wild-type (ATTRwt), would tolerate diflunisal with limited adverse events.

MATERIALS AND METHODS

This is a retrospective, longitudinal study of 23 patients with ATTR-CA (10 ATTRm and 13 ATTRwt) diagnosed at the Cleveland Clinic from May 2007 to August 2017 who were treated with diflunisal. Patients were prescribed diflunisal, fully informed of the risks of side effects. Patient characteristics and subsequent adverse events were recorded.

RESULTS

The duration of diflunisal therapy ranged from 1-89 months (median 15 months). Average eGFR at diflunisal initiation was 61.9 ± 15.4 mL/min/m². Only one patient had a transient rise in Cr of 0.31 mg/dL. There were no clinically significant bleeding events, despite most of the patients being on anticoagulants or antiplatelet agents. Three of 23 patients (13%) withdrew treatment due to drug side effects (erosive gastritis, epigastric pain and decreased appetite). No patients died or were hospitalized for heart failure.

CONCLUSION

Diflunisal was well-tolerated in both the ATTRm- and ATTRwt-CA populations. Withdrawal due to side effects was related to gastrointestinal complaints, but most patients had no adverse events. Diflunisal can be safely used in a selected group of ATTR-CA patients with appropriate clinical, renal and hematologic monitoring.

Evolution of thyroid hormone distributor proteins

Thyroid hormones (THs) are evolutionarily old hormones, having effects on metabolism in bacteria, invertebrates and vertebrates. THs bind specific distributor proteins (THDPs) to ensure their efficient distribution through the blood and cerebrospinal fluid in vertebrates. Albumin is a THDP in the blood of all studied species of vertebrates, so may be the original vertebrate THDP. However, albumin has weak affinity for THs. Transthyretin (TTR) has been identified in the blood across different lineages in adults vs juveniles. TTR has intermediate affinity for THs. Thyroxine-binding globulin has only been identified in mammals and has high affinity for THs. Of these THDPs, TTR is the only one known to be synthesised in the brain and is involved in moving THs from the blood into the cerebrospinal fluid. We analysed the rates of evolution of these three THDPs: TTR has been most highly conserved and albumin has had the highest rate of divergence.

Traversing barriers - How thyroid hormones pass placental, blood-brain and blood-cerebrospinal fluid barriers

Thyroid hormone is essential for normal human fetal growth and brain development. As the fetal thyroid does not secrete thyroid hormones until about 18 weeks gestation, early fetal brain development depends on passage of maternal hormone across the placenta into the fetal circulation. To reach the fetal brain, maternally derived and endogenously produced thyroid hormone has to cross the blood-brain and blood-cerebrospinal fluid barriers. In this review we will discuss the complex biological barriers (involving membrane transporters, enzymes and distributor proteins) that must be overcome to ensure that the developing human brain has adequate exposure to thyroid hormone.

MicroRNA regulation of Transthyretin in trophoblast differentiation and Intra-Uterine Growth Restriction

Placental trophoblast cells produce various cytokines, transporters vital to normal embryogenesis. Transthyretin (TTR) aids trans-placental passage of maternal thyroxin (TH) to fetal circulation. Inadequate TH delivery leads to developmental abnormality. Regulation of TTR biosynthesis in placenta is critical for normal embryo development. We showed here that TTR transcripts were expressed more in fetal placenta. Using bioinformatic analysis and confirmation with dual-luciferase reporter assays, we found that miR-200a-3p and miR-141-3p inhibited TTR expression by directly binding to the 3'UTR of TTR, which is reversed by mutation in the microRNA binding site. Differentiation of human trophoblast BeWo cells was associated with decreased TTR transcript and protein levels with concomitant increase in the levels of both microRNAs. Interestingly, ectopic overexpression of the microRNA mimics abrogated thyroxin uptake by BeWo cells, which was reversed by the corresponding inhibitors. Furthermore, in a rat model of intra-uterine growth restriction (IUGR), TTR expression decreased significantly in placenta with reciprocal rise in miR-141-3p but not 200a-3p. In human IUGR placenta, TTR transcript and protein levels were significantly lower associated with high expression of miR-141-3p but not 200a-3p. These data provides new insight into physiological role of miR-141-3p in regulating TTR during trophoblast differentiation and IUGR.

Aggregated transthyretin is specifically packaged into placental nano-vesicles in preeclampsia

In preeclampsia, the serum levels of transthyretin, a carrier protein for thyroxine, are elevated. Transthyretin isolated from preeclamptic serum is also aggregated and can induce preeclampsia-like symptoms in pregnant IL10^-/- mice. Using western blotting, immunofluorescence, ELISA and qRT-PCR, we investigated the production of transthyretin by preeclamptic placentae and whether transthyretin is carried into the maternal circulation via placental extracellular vesicles. Both total and aggregated transthyretin were present in higher levels in preeclamptic placentae compared to normotensive placentae (p < 0.05, n = 7), however the levels of transythretin mRNA were not significantly different (n = 8). Preeclamptic placentae secreted similar levels of total transthyretin compared to normotensive placentae (2352 ± 2949 ng/mL vs. 3250 ± 1864 ng/mL, mean ± SD, p > 0.05, n = 8), however in preeclampsia, a significant proportion is vesicle-associated (~48% vs 0%). Increased levels of aggregated transthyretin were specifically associated to preeclamptic nano-vesicles (p < 0.02, n = 8). This study showed that the placenta actively produces transthyretin and in preeclampsia, a significant amount is extruded into the maternal circulation via placental exracellular vesicles. The increased aggregation of transthyretin in preeclampsia occurs at the post-transcriptional level and while preeclamptic nano-vesicles may be removing a toxic aggregated protein from the placenta, they may also be delivering aggregated transthyretin to specific maternal organs, contributing to the pathogenesis of preeclampsia.

Targeting STOX1 in the therapy of preeclampsia

INTRODUCTION

Preeclampsia is a major pregnancy disease, explained partly by genetic predispositions. STOX1, a transcription factor discovered in 2005, was the first gene directly associated with genetic forms of the disease. Alterations of STOX1 expression as well as STOX1 variants have also been associated to Alzheimer's disease. These observations make of this gene a putative therapeutic target. Area covered: Two major isoforms (STOX1A and STOX1B) are encoded by the gene and are theoretically able to compete for the same binding site, while only the most complete (STOX1A) is supposed to be able to activate gene expression. This makes the ratio between STOX1A and STOX1B as well as their position inside the cell (nucleus or cytoplasm) crucial to understand how STOX1 functions. STOX1 appears to have multiple gene targets, especially in pathways connected to inflammation, oxidative stress, and cell cycle. Expert opinion: STOX1-directed therapies, could be directed either towards its targets (genes or pathways), or directly at STOX1. For this the addressing of STOX1 to various cell compartments could theoretically be modified; also it could be possible of altering the balance between the two isoforms, through selectively inhibiting one of them, possibly improving the outcomes in severe preeclampsia.

Increasing maternal obesity is associated with alterations in both maternal and neonatal thyroid hormone levels

OBJECTIVE

Obesity is associated with alterations in thyroid hormone (TH) levels in obese, pregnant individuals. The maintenance of TH levels throughout gestation is important for proper foetal development. The aim of this study was to measure levels of fT3, fT4 and TSH in maternal and matched cord blood serum from normal weight, overweight and obese gravidae to determine alterations in maternal and neonatal TH levels by virtue of maternal obesity.

DESIGN, SETTING, SUBJECTS, OUTCOME MEASURES

ELISA was utilized to measure fT3, fT4 and TSH levels from banked, matched maternal and neonatal (cord blood) serum (N = 205 matched pairs). Data were stratified according to prepregnancy or first trimester BMI.

RESULTS

Both maternal and neonatal fT3 levels consistently increased with increasing maternal obesity, and maternal and neonatal fT3 were significantly correlated (r = 0·422, P < 0·001). Maternal and neonatal fT3 were also significantly associated with birthweight (β = 0·155, P = 0·027 and β = 0·171, P = 0·018, respectively). Both the maternal and neonatal fT3 to fT4 ratio significantly increased with increasing maternal obesity. We further found that excess gestational weight gain was associated with a decrease in maternal fT4 compared with gravidae who had insufficient gestational weight gain (0·86 ± 0·17 vs 0·95 ± 0·22, P < 0·01).

CONCLUSION

Maternal obesity is not only associated with maternal alterations in TH, but with accompanying neonatal changes. Because both maternal obesity and alterations in TH levels are associated with childhood obesity, based on these findings and our prior analyses in a nonhuman primate model, we propose that changes in fT3 levels in the offspring of obese mothers may be a potential molecular mediator of foetal overgrowth and childhood obesity.

Prenatal Exposures to Multiple Thyroid Hormone Disruptors: Effects on Glucose and Lipid Metabolism

Background. Thyroid hormones (THs) are essential for normal human fetal development and play a major role in the regulation of glucose and lipid metabolism. Delivery of TH to target tissues is dependent on processes including TH synthesis, transport, and metabolism. Thyroid hormone endocrine disruptors (TH-EDCs) are chemical substances that interfere with these processes, potentially leading to adverse pregnancy outcomes. Objectives. This review focuses on the effects of prenatal exposures to combinations of TH-EDCs on fetal and neonatal glucose and lipid metabolism and also discusses the various mechanisms by which TH-EDCs interfere with other hormonal pathways. Methods. We conducted a comprehensive narrative review on the effects of TH-EDCs with particular emphasis on exposure during pregnancy. Discussion. TH imbalance has been linked to many metabolic processes and the effects of TH imbalance are particularly pronounced in early fetal development due to fetal dependence on maternal TH for proper growth and development. The pervasive presence of EDCs in the environment results in ubiquitous exposure to either single or mixtures of EDCs with deleterious effects on metabolism. Conclusions. Further evaluation of combined effects of TH-EDCs on fetal metabolic endpoints could improve advice provided to expectant mothers.

Understanding Pre-Eclampsia Using Alzheimer's Etiology: An Intriguing Viewpoint

Characterized by hypertension and proteinuria after the 20th week of gestation, pre-eclampsia (PE) is a major cause of maternal, fetal, and neonatal morbidity and mortality. Despite being recognized for centuries, PE still lacks a reliable, early means of diagnosis or prediction, and a safe and effective therapy. We have recently reported that the event of toxic protein misfolding and aggregation is a critical etiological manifestation in PE. Using comparative proteomic analysis of gestational age-matched sera from PE and normal pregnancy, we identified several proteins that appeared to be dysregulated in PE. Our efforts so far have focused on transthyretin (TTR), a transporter of thyroxine and retinol, and amyloid precursor protein whose aggregates were detected in the PE placenta. Based on these results and detection of TTR aggregates in sera from PE patients, we proposed that PE could be a disease of protein misfolding and aggregation. Protein misfolding and aggregation have long been linked with many neurodegenerative diseases such as Alzheimer's disease. However, linkage of protein misfolding and aggregation with the PE pathogenesis is a new and novel concept. This review aims to understand the roles of aggregated proteins in PE using the cues from the Alzheimer's etiology.

Exposure to Lithium and Cesium Through Drinking Water and Thyroid Function During Pregnancy: A Prospective Cohort Study

BACKGROUND

Impaired thyroid function is a common side effect of lithium medication. Recent data indicate that lithium exposure through drinking water, although providing much lower doses than the medication, may also affect thyroid hormone levels. However, the effects in susceptible groups like pregnant women are not known.

METHODS

In a population-based mother-child cohort in the Argentinean Andes (n = 194), an area with varying concentrations of lithium in the drinking water, we assessed lithium exposure repeatedly during pregnancy by measuring the concentrations in blood using inductively coupled plasma mass spectrometry. The markers of thyroid function included thyrotropin (TSH), free/total thyroxine (fT4/T4), free/total triiodothyronine (fT3/T3), thyroglobulin, and transthyretin in serum, sampled at the same time. Multiple potential confounders, including exposure to arsenic, cesium, and boron (elevated in water) as well as selenium and iodine (essential for thyroid function) were considered.

RESULTS

The lithium concentrations in blood [median 25 μg/L (0.0036 mmol/L); range 1.9-145 μg/L (0.000027-0.021 mmol/L)] correlated significantly with those in urine and drinking water (rs = 0.84, p < 0.001, and rs = 0.40, p < 0.001, respectively). Using linear quantile regression models, we found a positive association between blood lithium (log2 transformed) and TSH concentrations, particularly in the lowest percentiles of TSH (B = 0.20 mIU/L, [95% confidence interval 0.048-0.35] at the fifth percentile). We also found inverse associations of blood lithium with transthyretin, particularly at the highest percentiles, as well as with fT3 and T3, with less obvious variation across percentiles. Unexpectedly, blood cesium concentrations (median 111 μg/L, range 2.5-711 μg/L) were also inversely associated with fT3 and T3, particularly at the highest T3 percentiles, but not with TSH or transthyretin. Arsenic and boron exposure (also through drinking water) did not show any associations with the thyroid parameters.

CONCLUSIONS

The study supports previous findings that lithium exposure through drinking water may impair thyroid function. The results regarding cesium exposure through drinking water are new. During pregnancy, impaired thyroid function may be detrimental for fetal development. The findings reinforce the need for better control of drinking water, including bottled water, as well as a health-based guideline value.

Impact of endocrine-disrupting chemicals on thyroid function and brain development

Endocrine disrupting chemicals (EDCs) are synthetic or natural substances in the environment. EDCs have been shown to disrupt reproductive, developmental and other homeostatic systems by interfering with the synthesis, secretion, transport, metabolism and action of endogenous hormones including the thyroid hormone (TH) system. Since TH plays a critical role in brain development, the exposure to TH-system disrupting EDCs during development may have serious consequences. In this article, representative previous studies showing the effect of representative EDCs on the TH system are summarized. Then, the molecular mechanisms of action of polychlorinated biphenyls and polybrominated diphenyl ethers on the TH system are discussed further. Particularly, the effect of polychlorinated biphenyls and polybrominated diphenyl ethers on TH-mediated brain development is discussed. Our recent studies may provide a novel idea regarding the effect of EDCs on the TH system.

Proteome differences in the first- and third-trimester human placentas

Placenta is a transient and unique pregnancy tissue that supports the fetus nutritionally and metabolically. Expression of the unique placental proteins in different stages may influence the development of the fetus as well as the pregnancy outcome. The present study aimed to compare the total placental proteome differences between the normal first- and third-trimester human placentas. In the current study, placental proteome was compared between normal first- and third-trimester placentas using 2-dimensional polyacrylamide gel electrophoresis method for separation and matrix-assisted laser desorption/ionization time-of flight mass spectrometry technique for identification of the proteins. Despite the overall similarities, comparison of the mean intensity of the protein spots between the first- and third-trimester placental proteomes revealed that 22 spots were differentially expressed (P < .05) among which 11 distinct spots were successfully identified. Of the 11 differentially expressed proteins, 4 were increased (protein disulfide isomerase, tropomyosin 4 isoform 2, enolase 1, and 78-kDa glucose-regulated protein), while the remaining 7 (actin γ1 propeptide, heat shock protein gp96, α1-antitrypsin, EF-hand domain family member D1, tubulin α1, glutathione S-transferase, and vitamin D binding protein) showed decreased expression in the placentas from the first-trimester compared to the full-term ones. In summary, the results of the present study as the first research on the comparison of the first- and third-trimester human placental proteomes introduced a group of 11 proteins with altered expression. Interestingly, some of these proteins are reported to be altered in pregnancy-related disorders.

Molecular basis of thyrotropin and thyroid hormone action during implantation and early development

BACKGROUND

Implantation and early embryo development are finely regulated processes in which several molecules are involved. Evidence that thyroid hormones (TH: T4 and T3) might be part of this machinery is emerging. An increased demand for TH occurs during gestation, and any alteration in maternal thyroid physiology has significant implications for both maternal and fetal health. Not only overt but also subclinical hypothyroidism is associated with infertility as well as with obstetric complications, including disruptions and disorders of pregnancy, labor, delivery, and troubles in early neonatal life.

METHODS

We searched the PubMed and Google Scholar databases for articles related to TH action on ovary, endometrium, trophoblast maturation and embryo implantation. In addition, articles on the regulation of TH activity at cellular level have been reviewed. The findings are hereby summarized and critically discussed.

RESULTS

TH have been shown to influence endometrial, ovarian and placental physiology. TH receptors (TR) and thyrotropin (thyroid-stimulating hormone: TSH) receptors (TSHR) are widely expressed in the feto-maternal unit during implantation, and both the endometrium and the trophoblast might be influenced by TH either directly or through TH effects on the synthesis and activity of implantation-mediating molecules. Interestingly, due to the multiplicity of mechanisms involved in TH action (e.g. differential expression of TR isoforms, heterodimeric receptor partners, interacting cellular proteins, and regulating enzymes), the TH concentration in blood is not always predictive of their cellular availability and activity at both genomic and nongenomic level.

CONCLUSIONS

In addition to the known role of TH on the hormonal milieu of the ovarian follicle cycle, which is essential for a woman's fertility, evidence is emerging on the importance of TH signaling during implantation and early pregnancy. Based on recent observations, a local action of TH on female reproductive organs and the embryo during implantation appears to be crucial for a successful pregnancy. Furthermore, an imbalance in the spatio-temporal expression of factors involved in TH activity might induce early arrest of pregnancy in women considered as euthyroid, based on their hormonal blood concentration. In conclusion, alterations of the highly regulated local activity of TH may play a crucial, previously underestimated, role in early pregnancy and pregnancy loss. Further studies elucidating this topic should be encouraged.

Transthyretin: a multifaceted protein

Transthyretin is a highly conserved homotetrameric protein, mainly synthetized by the liver and the choroid plexus of brain. The carrier role of TTR is well-known; however, many other functions have emerged, namely in the nervous system. Behavior, cognition, neuropeptide amidation, neurogenesis, nerve regeneration, axonal growth and 14-3-3ζ metabolism are some of the processes where TTR has an important role. TTR aggregates are responsible for many amyloidosis such as familial amyloidotic polyneuropathy and cardiomyopathy. Normal TTR can also aggregate and deposit in the heart of old people and in preeclampsia placental tissue. Differences in TTR levels have been found in several neuropathologies, but its neuroprotective role, until now, was described in ischemia and Alzheimer’s disease. The aim of this review is to stress the relevance of TTR, besides its well-known role on transport of thyroxine and retinol-binding protein.

Transthyretin as a novel candidate biomarker for preeclampsia

Preeclampsia (PE) is considered to be a potentially fatal complication during pregnancy. However, no effective laboratory assessment has been developed to enable early diagnosis and monitoring of PE. The present study aimed to identify differentially expressed transthyretin (TTR) during severe PE and evaluate TTR as a possible biomarker of this disease. TTR levels were determined in the different gestational weeks of normal pregnancy (before 20 weeks, n=41; after 20 weeks, n=39) using enzyme-linked immunosorbent assay (ELISA). TTR concentrations in pregnant females with severe PE (n=43) were compared with those in healthy matched control subjects (n=37) using western blot analysis and ELISA. The median TTR concentration during severe PE in each month of gestation was significantly lower than the concentrations recorded during normal pregnancy. TTR levels in females with severe PE were significantly downregulated compared with the control subjects (P<0.001; area under the curve, 0.834-0.967). Thus, TTR may be used as a potential biomarker of PE.

Transthyretin is dysregulated in preeclampsia, and its native form prevents the onset of disease in a preclinical mouse model

Preeclampsia is a major pregnancy complication with potential short- and long-term consequences for both mother and fetus. Understanding its pathogenesis and causative biomarkers is likely to yield insights for prediction and treatment. Herein, we provide evidence that transthyretin, a transporter of thyroxine and retinol, is aggregated in preeclampsia and is present at reduced levels in sera of preeclamptic women, as detected by proteomic screen. We demonstrate that transthyretin aggregates form deposits in preeclampsia placental tissue and cause apoptosis. By using in vitro approaches and a humanized mouse model, we provide evidence for a causal link between dysregulated transthyretin and preeclampsia. Native transthyretin inhibits all preeclampsia-like features in the humanized mouse model, including new-onset proteinuria, increased blood pressure, glomerular endotheliosis, and production of anti-angiogenic factors. Our findings suggest that a focus on transthyretin structure and function is a novel strategy to understand and combat preeclampsia.

Mild iodine deficiency in pregnancy in Europe and its consequences for cognitive and psychomotor development of children: a review

Despite the introduction of salt iodization programmes as national measures to control iodine deficiency, several European countries are still suffering from mild iodine deficiency (MID). In iodine sufficient or mildly iodine deficient areas, iodine deficiency during pregnancy frequently appears in case the maternal thyroid gland cannot meet the demand for increasing production of thyroid hormones (TH) and its effect may be damaging for the neurodevelopment of the foetus. MID during pregnancy may lead to hypothyroxinaemia in the mother and/or elevated thyroid-stimulating hormone (TSH) levels in the foetus, and these conditions have been found to be related to mild and subclinical cognitive and psychomotor deficits in neonates, infants and children. The consequences depend upon the timing and severity of the hypothyroxinaemia. However, it needs to be noted that it is difficult to establish a direct link between maternal iodine deficiency and maternal hypothyroxinaemia, as well as between maternal iodine deficiency and elevated neonatal TSH levels at birth. Finally, some studies suggest that iodine supplementation from the first trimester until the end of pregnancy may decrease the risk of cognitive and psychomotor developmental delay in the offspring.