Carrier-mediated thyroid hormone transport into placenta by placental transthyretin

Human placental transthyretin in fetal growth restriction in combination with preeclampsia and the HELLP syndrome

Fetal growth restriction is a serious, still poorly understood pregnancy-related pathology often associated with preeclampsia. Recent studies speculate on the role of human transthyretin, a carrier protein for thyroxin and retinol binding protein, in the etiology of both pregnancy pathologies. Objective was to investigate the localization and abundance of transthyretin (TTR) in placentas of pregnancies suffering from fetal growth restriction with and without preeclampsia and HELLP. This was a retrospective case control study on human paraffin-embedded placentas from pregnancies with a gestational age at delivery between the 24th and 34th week of gestation. 16 placentas were included in this study, 11 cases and 5 from normotensive pregnancies as controls. Cases were divided into three groups: four from early onset idiopathic intrauterine growth restriction (IUGR), four from early-onset severe preeclampsia (PE), and three from early-onset IUGR with preeclampsia plus HELLP syndrome. Distribution and abundance of TTR were investigated by means of immunohistochemistry. Semi quantitative analysis of TTR staining of placental sections revealed that TTR was mostly expressed in the villous trophoblast covering placental villi. Only weak staining of TTR in villous stroma could be detected. The comparison of placentas revealed that in pure IUGR and severe PE there is a much stronger TTR reactivity compared to controls and cases with IUGR + PE + HELLP. Concluding, the study showed that TTR is dysregulated in cases of IUGR and severe early onset preeclampsia. Interestingly, TTR expression is not affected in cases with HELLP syndrome that reveal the same staining intensities as age-matched controls.

Effects of chronic stress on prefrontal cortex transcriptome in mice displaying different genetic backgrounds

There is increasing evidence that depression derives from the impact of environmental pressure on genetically susceptible individuals. We analyzed the effects of chronic mild stress (CMS) on prefrontal cortex transcriptome of two strains of mice bred for high (HA)and low (LA) swim stress-induced analgesia that differ in basal transcriptomic profiles and depression-like behaviors. We found that CMS affected 96 and 92 genes in HA and LA mice, respectively. Among genes with the same expression pattern in both strains after CMS, we observed robust upregulation of Ttr gene coding transthyretin involved in amyloidosis, seizures, stroke-like episodes, or dementia. Strain-specific HA transcriptome affected by CMS was associated with deregulation of genes involved in insulin secretion (Acvr1c, Nnat, and Pfkm), neuropeptide hormone activity (Nts and Trh), and dopamine receptor mediated signaling pathway (Clic6, Drd1a, and Ppp1r1b). LA transcriptome affected by CMS was associated with genes involved in behavioral response to stimulus (Fcer1g, Rasd2, S100a8, S100a9, Crhr1, Grm5, and Prkcc), immune effector processes (Fcer1g, Mpo, and Igh-VJ558), diacylglycerol binding (Rasgrp1, Dgke, Dgkg, and Prkcc), and long-term depression (Crhr1, Grm5, and Prkcc) and/or coding elements of dendrites (Crmp1, Cntnap4, and Prkcc) and myelin proteins (Gpm6a, Mal, and Mog). The results indicate significant contribution of genetic background to differences in stress response gene expression in the mouse prefrontal cortex.

Proteomic evaluation of sheep serum proteins

BACKGROUND

The applications of proteomic strategies to ovine medicine remain limited. The definition of serum proteome may be a good tool to identify useful protein biomarkers for recognising sub-clinical conditions and overt disease in sheep. Findings from bovine species are often directly translated for use in ovine medicine. In order to characterize normal protein patterns and improve knowledge of molecular species-specific characteristics, we generated a two-dimensional reference map of sheep serum. The possible application of this approach was tested by analysing serum protein patterns in ewes with mild broncho-pulmonary disease, which is very common in sheep and in the peripartum period which is a stressful time, with a high incidence of infectious and parasitic diseases.

RESULTS

This study generated the first reference 2-DE maps of sheep serum. Overall, 250 protein spots were analyzed, and 138 identified.Compared with healthy sheep, serum protein profiles of animals with rhino-tracheo-bronchitis showed a significant decrease in protein spots identified as transthyretin, apolipoprotein A1 and a significant increase in spots identified as haptoglobin, endopin 1b and alpha1B glycoprotein.In the peripartum period, haptoglobin, alpha-1-acid glycoprotein, apolipoprotein A1 levels rose, while transthyretin content dropped.

CONCLUSIONS

This study describes applications of proteomics in putative biomarker discovery for early diagnosis as well as for monitoring the physiological and metabolic situations critical for ovine welfare.

Transthyretin: roles in the nervous system beyond thyroxine and retinol transport

Transthyretin (TTR) is a plasma- and cerebrospinal fluid-circulating protein. Besides the primordially attributed systemic role as a transporter molecule of thyroxine (T₄) and retinol (through the binding to retinol-binding protein [RBP]), TTR has been recognized as a protein with important functions in several aspects of the nervous system physiology. TTR has been shown to play an important role in behavior, cognition, amidated neuropeptide processing and nerve regeneration. Furthermore, it has been proposed that TTR is neuroprotective in Alzheimer's disease and cerebral ischemia. Mutations in TTR are a well-known cause of familial amyloidotic polyneuropathy, an autosomal dominant neurodegenerative disorder characterized by systemic deposition of TTR amyloid fibrils, particularly in the peripheral nervous system. The purpose of this review is to highlight the roles of TTR in the nervous system, beyond its systemic role as a transporter molecule of T₄ and RBP-retinol.

Expression and uptake of the thyroxine-binding protein transthyretin is regulated by oxygen in primary trophoblast placental cells

Transplacental delivery of maternal thyroid hormones to the fetus, in particular thyroxine (T₄), is critical in ensuring normal fetal neurological development. The fetus relies on maternal T₄ till around 16 weeks gestation, but mechanisms of placental T₄ transport are not yet fully elucidated. Placenta produces, secretes and takes up the thyroid hormone-binding protein transthyretin (TTR). Many placental genes are regulated by oxygen levels, which are relatively low (1%) in the early first trimester, rising to 3% in the mid first trimester and 8% in the early second trimester and thereafter. We examined the expression and uptake of TTR in isolated primary human placental cytotrophoblast cells cultured under different oxygen concentrations (1, 3, 8, 21% O₂ and 200 μM desferrioxamine (DFO)) for 24 h. We observed sevenfold higher expression of TTR mRNA and protein levels at 1% O₂ than at 8 and 21% O₂. Significant increases were observed after culture at 3% O₂ and following DFO treatment. We observed significantly higher uptake of ¹²⁵I-TTR and Alexa-594-TTR when cells were cultured at 1 and 3% O₂ and in the presence of 200 μM DFO than at 8 and 21% O₂. When JEG-3 choriocarcinoma cells were transfected with TTR promoter reporter constructs, increased luciferase activity was measured in cells cultured at 1 and 3% O₂ in comparison to 8 and 21% O₂. We conclude that placental TTR expression and uptake is increased by the relative hypoxia observed in the first trimester of pregnancy, a time when materno-fetal T₄ transfer is the sole source of fetal T₄.

Levels and patterns of hydroxylated polychlorinated biphenyls (OH-PCBs) and their associations with thyroid hormones in hooded seal (Cystophora cristata) mother-pup pairs

Blood (plasma/serum) samples from 14 adult female and their pups (1-4 days old) captured in the West Ice, east of Greenland were analysed for concentrations of total and free thyroxine and triiodothyronine (TT4, FT4, TT3, FT3), and hydroxylated polychlorinated biphenyls (OH-PCBs). The levels of all thyroid hormones (THs) were significantly higher in pups than in mothers. Sum OH-PCB levels (ΣOH-PCBs: 4-OH-CB107, 3'-OH-CB138, 4-OH-CB146, 4'-OH-CB172, 4-OH-CB187) were significantly higher in mothers (3.98 ± 1.55 pmol/g; 1.40 ± 0.54 ng/g wet weight) as compared to pups (1.95 ± 0.78 pmol/g; 0.68 ± 0.28 ng/g wet weight). Plasma levels of TT4 and FT4 in mothers increased as a function of pup age, as did levels of individual OH-PCBs in both mothers and pups. The pattern of OH-PCBs in the pups was similar to their mothers. We suggest that OH-PCBs found in pups are transferred from their mothers during gestation and that the transfer also continues after parturition via milk. Principal component analysis (PCA) showed that in pups, 4-OH-CB107 and 3'-OH-CB138 were negatively associated with FT4:FT3 and TT3:FT3 ratios, respectively. These relationships were confirmed by partial correlation analysis correcting for pup age. PCA suggested that 4'-OH-CB172 and 4-OH-CB187 were negatively associated with TT3 in mothers. However, this was not confirmed by correlation tests. Although statistical relationships should be interpreted with caution, the study indicates that young developing seals are more sensitive compared to adults with respect to TH-related effects of OH-PCBs.

Ontogenic changes in placental transthyretin

OBJECTIVES

Before secretion of fetal thyroid hormone at around 16 weeks gestation normal fetal development depends on a constant supply of maternal thyroid hormone (TH), particularly thyroxine (T(4)). The detailed mechanisms of transplacental delivery of TH are still uncertain. The TH binding protein, transthyretin (TTR), is produced and secreted by placenta and may play a role in this process. The ontogeny of placental TTR is unknown. Our aim was to study changes in placental TTR in early and late pregnancy.

STUDY DESIGN

We collected placentas from surgically terminated pregnancies between 6 and 17 weeks gestation (n = 44) and from normal term (38-39 weeks) pregnancies following caesarean section (n = 5). Real time-PCR, western blotting and immunohistochemistry were used to determine TTR mRNA and protein levels.

RESULTS

There were highly significant correlations between gestational age and TTR mRNA (r = 0.974; p < 0.0001) and between gestational age and TTR protein (r = 0.901; p < 0.001) levels between weeks 6 and 13 of gestation. TTR expression did not increase between 13 and 17 weeks and was not different at term. Good correlation was observed between TTR mRNA and TTR protein between individual placental samples (r = 0.916; p < 0.0001). A similar trend was observed using immunohistochemical staining of placental paraffin sections.

CONCLUSIONS

Our results demonstrate that TTR is expressed in the human placenta from at least 6 weeks gestation. Levels rise during the first trimester at a time when placental oxygen tensions are also rising. We hypothesise that TTR production and secretion by the placenta may facilitate transplacental delivery of TH to the fetus.

Polybrominated diphenyl ethers, hydroxylated polybrominated diphenyl ethers, and measures of thyroid function in second trimester pregnant women in California

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) may disrupt thyroid function and contribute to adverse neurodevelopmental outcomes. We conducted a pilot study to explore the relationship between serum concentrations of lower-brominated PBDEs (BDE-17 to -154), higher-brominated PBDEs (BDE-183 to -209), and hydroxylated PBDE metabolites (OH-PBDEs) with measures of thyroid function in pregnant women. Concentrations of PBDEs, OH-PBDEs, thyroid-stimulating hormone (TSH), total thyroxine (T(4)), and free T(4) were measured in serum samples collected between 2008 and 2009 from 25 second trimester pregnant women in California. Median concentrations of lower-brominated PBDEs and OH-PBDEs were the highest reported to date in pregnant women. Median concentrations of BDE-47 and the sum of lower-brominated PBDEs (ΣPBDE(5)) were 43.1 ng/g lipid and 85.8 ng/g lipid, respectively, and the sum of OH-PBDEs (ΣOH-PBDE(4)) was 0.084 ng/mL. We observed a positive association between the weighted sum of chemicals known to bind to transthyretin (ΣTTR binders) and TSH levels. We also found positive associations between TSH and ΣPBDE(5), ΣOH-PBDE(4), BDE-47, BDE-85, 5-OH-BDE47, and 4'-OH-BDE49, and an inverse association with BDE-207. Relationships with free and total T(4) were weak and inconsistent. Our results indicate that PBDE exposures are elevated in pregnant women in California and suggest a relationship with thyroid function. Further investigation is warranted to characterize the risks of PBDE exposures during pregnancy.

Thyroid hormone regulates the expression of the sonic hedgehog signaling pathway in the embryonic and adult Mammalian brain

Thyroid hormone is important for development and plasticity in the immature and adult mammalian brain. Several thyroid hormone-responsive genes are regulated during specific developmental time windows, with relatively few influenced across the lifespan. We provide novel evidence that thyroid hormone regulates expression of the key developmental morphogen sonic hedgehog (Shh), and its coreceptors patched (Ptc) and smoothened (Smo), in the early embryonic and adult forebrain. Maternal hypo- and hyperthyroidism bidirectionally influenced Shh mRNA in embryonic forebrain signaling centers at stages before fetal thyroid hormone synthesis. Further, Smo and Ptc expression were significantly decreased in the forebrain of embryos derived from hypothyroid dams. Adult-onset thyroid hormone perturbations also regulated expression of the Shh pathway bidirectionally, with a significant induction of Shh, Ptc, and Smo after hyperthyroidism and a decline in Smo expression in the hypothyroid brain. Short-term T₃ administration resulted in a significant induction of cortical Shh mRNA expression and also enhanced reporter gene expression in Shh(+/LacZ) mice. Further, acute T₃ treatment of cortical neuronal cultures resulted in a rapid and significant increase in Shh mRNA, suggesting direct effects. Chromatin immunoprecipitation assays performed on adult neocortex indicated enhanced histone acetylation at the Shh promoter after acute T₃ administration, providing further support that Shh is a thyroid hormone-responsive gene. Our results indicate that maternal and adult-onset perturbations of euthyroid status cause robust and region-specific changes in the Shh pathway in the embryonic and adult forebrain, implicating Shh as a possible mechanistic link for specific neurodevelopmental effects of thyroid hormone.

Delivery of maternal thyroid hormones to the fetus

Thyroid hormones (THs) play an essential role in ensuring normal fetal development, particularly that of the central nervous system. Before 16 weeks gestation, the fetus relies solely on transplacental delivery of maternal T(4), and clinical studies suggest that even mild maternal thyroid hormone deficiency adversely affects the intellectual function of offspring. Maternofetal TH transfer is regulated by trophoblast cell membrane transporters, which mediate influx and efflux of THs, placental deiodinases D3 and D2, which control intraplacental TH levels, and TH-binding proteins (transthyretin), which provide transport roles in the placenta. This review discusses new information about mechanisms of transplacental delivery of T(4) to the fetus, providing insight into complex processes that are vitally important for normal fetal development.

Polybrominated diphenyl ethers and their hydroxylated/methoxylated analogs: environmental sources, metabolic relationships, and relative toxicities

Brominated compounds are ubiquitous in the aquatic environment. The polybrominated diphenyl ether (PBDE) flame retardants are anthropogenic compounds of concern. Studies suggest that PBDEs can be biotransformed to hydroxylated brominated diphenyl ethers (OH-BDE). However, the rate of OH-BDE formation observed has been extremely small. OH-BDEs have also been identified as natural compounds produced by some marine invertebrates. Another class of compounds, the methoxylated BDEs (MeO-BDEs), has also been identified as natural compounds in the marine environment. Both the OH-BDEs and MeO-BDEs bioaccumulate in higher marine organisms. Recent studies have demonstrated that MeO-BDEs can be biotransformed to OH-BDEs and this generates greater amounts of OH-BDEs than could be generated from PBDEs. Consequently, MeO-BDEs likely represent the primary source of metabolically derived OH-BDEs. Given that for some endpoints OH-BDEs often exhibit greater toxicity compared to PBDEs, it is prudent to consider OH-BDEs as chemicals of concern, despite their seemingly "natural" origins.

Multifactorial analysis of affinity-mass spectrometry data from serum protein samples: a strategy to distinguish patients with preeclampsia from matching control individuals

A multifactorial differential analysis of serum proteins using mass spectrometry distinguished samples from pregnant women with severe early-onset preeclampsia (n = 11) from those of control individuals with uneventful pregnancies (n = 13). Serum proteins were fractionated by either their affinities to reversed-phase material coated magnetic beads or by fractionated precipitation. The on-average most abundant ion signals were observed at m/z 9390, 9103, and 8886. The best differentiating ion signals between the two sample groups were found at m/z 13,715, 13,834, and 13,891. The normalized intensities of these ion signals were on-average lower in the preeclampsia group than in the control group. The six ion signal intensities enabled sorting of the individual spectra with high accuracy. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that a protein band migrating just above the 14 kDa marker band contained transthyretin (P02766; M(r) (avg.): 13,761). Densitometric analysis of the transthyretin bands showed lower intensities in the preeclampsia samples with respect to those of the controls. Nephelometric analysis of the serum samples determined the mean concentration of transthyretin in the preeclampsia group were lower (0.16 mg/mL; range: 0.13 to 0.20; SD: 0.03) than that in the control group (0.19 mg/mL; range: 0.14 to 0.22; SD: 0.02), substantiating the role of transthyretin concentration differences in the comparison of the two groups. Altogether, our findings support the theory of preeclampsia being a heterogeneous disorder that might be sub-classified by a defined proteome signature in maternal blood using multifactorial analysis of affinity-fractionated serum samples.

Hydroxylated polybrominated diphenyl ethers and bisphenol A in pregnant women and their matching fetuses: placental transfer and potential risks

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are suspected endocrine disruptors, which can pass through the mammalian placenta and accumulate in the human maternal-fetal-placental unit. However, little is known about mechanisms of placental transfer and the associated risk(s). Ten OH-PBDE congeners, bisphenol A (BPA), total 17beta-estradiol (E2), and total thyroxine (T4) were quantified in blood serum from 26 pregnant women and 28 matching fetuses, including three pairs of twins from South Korea. Only 6-OH-BDE-47, a naturally occurring OH-PBDE, was detected at relatively great concentrations (maternal serum: 17.5 +/- 26.3 pg/g ww, fetal cord blood serum: 30.2 +/- 27.1 pg/g ww), which suggests that exposure was related to diets among Korean women. Concentrations of 6-OH-BDE-47 in maternal and cord serum were positively correlated, with concentrations being significantly greater in cord blood serum. The placental transfer ratio between fetal and maternal blood serum for 6-OH-BDE-47 (F/M ratio: 1.4 +/- 1.1) was different than the observed placental transfer ratio of BPA and previously reported values for hydroxylated polychlorinated biphenyls (OH-PCBs). This result is possibly due to large affinities to T4 transport proteins. Lesser concentrations of E2 and T4 were detected in cord blood serum (E2: 4.7 +/- 2.2 ng/mL, T4: 8.5 +/- 1.7 microg/dL) compared to maternal blood serum (E2: 8.0 +/- 3.0 ng/mL, T4: 9.7 +/- 1.8 microg/dL). A major effect of OH-PBDE exposure might be a decrease in serum T4 concentrations. Potential risks associated with disruption of T4 transport to the developing fetus such as negative consequences for fetal neurological development should be considered in further studies.