Ontogenic changes in placental transthyretin

Protein Misfolding in Pregnancy: Current Insights, Potential Mechanisms, and Implications for the Pathogenesis of Preeclampsia

Protein misfolding disorders are a group of diseases characterized by supra-physiologic accumulation and aggregation of pathogenic proteoforms resulting from improper protein folding and/or insufficiency in clearance mechanisms. Although these processes have been historically linked to neurodegenerative disorders, such as Alzheimer's disease, evidence linking protein misfolding to other pathologies continues to emerge. Indeed, the deposition of toxic protein aggregates in the form of oligomers or large amyloid fibrils has been linked to type 2 diabetes, various types of cancer, and, in more recent years, to preeclampsia, a life-threatening pregnancy-specific disorder. While extensive physiological mechanisms are in place to maintain proteostasis, processes, such as aging, genetic factors, or environmental stress in the form of hypoxia, nutrient deprivation or xenobiotic exposures can induce failure in these systems. As such, pregnancy, a natural physical state that already places the maternal body under significant physiological stress, creates an environment with a lower threshold for aberrant aggregation. In this review, we set out to discuss current evidence of protein misfolding in pregnancy and potential mechanisms supporting a key role for this process in preeclampsia pathogenesis. Improving our understanding of this emerging pathophysiological process in preeclampsia can lead to vital discoveries that can be harnessed to create better diagnoses and treatment modalities for the disorder.

Prenatal exposure to emerging and traditional organophosphate flame retardants: Regional comparison, transplacental transfer, and birth outcomes

During gestation, organophosphate flame retardants (OPFRs) have the potential to pose health risks to fetuses due to their ability to cross the placental barrier. However, data are scarce regarding the transplacental transfer of these compounds, particularly concerning emerging OPFRs and regional variations. In this study, we analyzed 14 traditional OPFRs and 5 emerging OPFRs in maternal and cord serum samples from Mianyang and Hangzhou, two cities in eastern and western China, respectively. The results revealed marked disparities in the overall levels of OPFRs between the two cities (p < 0.05), with the average concentration in maternal serum being higher in Hangzhou (14.55 ng/mL) than in Mianyang (8.28 ng/mL). The most abundant compounds found in both cities were tris (2-chloroethyl) phosphate (TCEP), Triphenyl phosphate (TPHP), and Tri-n-butyl phosphate (TnBP). Additionally, this study marked the first detection of novel OPFRs, including resorcinol bis (diphenyl phosphate) (RDP), isodecyl diphenyl phosphate (IDDPP), cresyl diphenyl phosphate (CDP), and bisphenol A bis (diphenyl phosphate) (BPA-BDPP) in maternal and cord serum simultaneously with the detection frequencies higher than 45%. This study also found that transplacental transfer efficiencies for OPFRs varied by ester group, with Aryl-OPFRs exhibiting the highest transfer rates (0.90-1.11) and Alkyl-OPFRs exhibiting the lowest (0.66-0.83). Transfer efficiencies exhibited a positive correlation with log Kow values (p < 0.05), suggesting that hydrophobic OPFRs with higher log Kow values are more likely to permeate the placental barrier. Moreover, the exposure levels of Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), Tri (Chloropropyl) Phosphate (TCIPP), TPHP, and CDP in cord serum were negatively associated (p < 0.05) with birthweight of newborns. This research adds to our understanding of the transplacental transfer of OPFRs and the possible health risks associated with prenatal exposure.

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.

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.

Preconception thyroid-stimulating hormone levels and adverse pregnancy outcomes

OBJECTIVE

Evidence for the association between subclinical thyroid dysfunction before conception and its pregnancy outcomes is inconsistent. Thus, we evaluated the relationship between preconception thyroid-stimulating hormone (TSH) levels and adverse pregnancy outcomes.

DESIGN

Retrospective cohort study.

METHODS

A total of 50,217 women without prior thyroid disease who became pregnant within 1 year after undertaking a routine TSH test in the Chongqing Municipality of China (2010-2016) were studied. Restricted cubic spline regression and logistic regression were used to estimate the association between preconception TSH levels and pregnancy outcomes. The main outcomes were individual and composite adverse pregnancy outcomes (CAPOs) comprising pregnancy loss, small for gestational age, large for gestational age, and preterm birth.

RESULTS

Incidence of CAPO was 24.19%. Increased preconception TSH level was positively associated with CAPO (odds ratio [OR]/SD: 1.04, 95% confidence interval [CI]: 1.01-1.07) when TSH was ≥2.1 mIU/L, positively associated with pregnancy loss (OR/SD: 1.06, 95% CI: 1.01-1.12) when TSH was <2.1 mIU/L, negatively and positively associated with preterm delivery when TSH levels were <1.3 mIU/L (OR/SD: 0.90, 95% CI: 0.83-0.97) and >3.0 mIU/L (OR/SD: 1.08, 95% CI: 1.00-1.17), respectively. Women with subclinical hypothyroidism before conception were at a higher risk for CAPO (adjusted odds ratio [aOR]: 1.12, 95% CI: 1.04-1.22), while those with subclinical hyperthyroidism had a higher risk of preterm delivery (aOR: 1.31, 95% CI: 1.01-1.70).

CONCLUSIONS

Nonlinear associations were indicated between preconception TSH levels and pregnancy outcomes. Subclinical thyroid dysfunction before conception was associated with an increased risk of adverse pregnancy outcomes.

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.

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.

Transplacental Behaviors of Organophosphate Tri- and Diesters Based on Paired Human Maternal and Cord Whole Blood: Efficiencies and Impact Factors

Organophosphate tri- and diesters (tri-OPEs and di-OPEs) were quantified in 63 paired maternal and cord whole blood samples collected in Hubei, China, in which tri-o-cresyl phosphate (ToCP) was predominant. The transplacental transfer efficiencies (expressed as cord blood to maternal blood (C:M) concentration ratios) of aryl-tri-OPEs, such as ToCP (1.61) and triphenyl phosphate (TPHP) (1.06), were higher than those of alkyl-tri-OPEs (0.66-0.76). For the target tri-OPEs and some traditional organic compounds, the C:M ratios first increased with log K_ow in the range of 1.63-5.23 and then decreased, showing a parabolic relationship. However, ToCP, with a log K_ow of 6.34, deviated from this relationship and displayed the highest C:M ratio (1.61). Molecular docking indicated a very strong binding affinity between ToCP and transthyretin, suggesting that ToCP might be actively transported by transthyretin in the placenta. The di-OPE levels in the blood samples were significantly lower than the corresponding tri-OPE levels, and those in the cord blood were influenced not only by their transplacental behaviors but also by their low excretion rates and the metabolic characteristics of their parent compounds in the fetus. This study provides useful information for accurately assessing the health risks posed by tri-OPEs to pregnant women and fetuses.

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.

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.

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.

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.

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.

Preeclampsia is associated with low placental transthyretin levels

OBJECTIVE

To investigate the relationship between placental transthyretin (TTR) level and preeclampsia.

MATERIALS AND METHODS

Placental tissues from uncomplicated and preeclamptic pregnancies were analyzed using immunohistochemistry and image analysis. We measured the mean optical density (OD) of immunohistochemical staining of TTR across multiple sections using Image Pro Plus 6.0. To avoid bias, we used placental tissue array, which contained preeclamptic placentas (n=8) and the control placentas (n=6) on the same slide.

RESULTS

The mean TTR OD of the syncytiotrophoblast layer of placentas (95% confidence interval) from the first trimester was higher than those from the second/third trimester, and term placentas [0.149 (0.014-0.285) for the 1(st) trimester, 0.037 (0.000-0.073) for the 2(nd)/3(rd) trimester, and 0.011 (0.035-0.056) for term; p<0.01]. Although the OD of the second/third trimester placentas appeared greater than that of term placentas, this was not statistically significant. The mean TTR OD of the syncytiotrophoblast layer of the severe preeclampsia group was lower than that of controls [0.010 (0.005-0.016) vs. 0.027 (0.013-0.041), p<0.05].

CONCLUSION

The immunohistochemical expression of TTR in the syncytiotrophoblast layer of the placenta decreased significantly after 12 weeks of gestation, paralleling the changing demands of thyroid hormone uptake into the placenta. The reduced TTR expression in the syncytiotrophoblast layer of the preeclamptic placenta might impair thyroid hormone uptake and contribute to the pathophysiology of the disease.

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.

Comparative expression of hCG β-genes in human trophoblast from early and late first-trimester placentas

Human chorionic gonadotropin (hCG) displays a major role in pregnancy initiation and progression and is involved in trophoblast differentiation and fusion. However, the site and the type of dimeric hCG production during the first trimester of pregnancy is poorly known. At that time, trophoblastic plugs present in the uterine arteries disappear, allowing unrestricted flow of maternal blood to the intervillous space. The consequence is an important modification of the trophoblast environment, including a rise of oxygen levels from about 2.5% before 10 wk of amenorrhea (WA) to ∼8% after 12 WA. Two specific β-hCG proteins that differ from three amino acids have been described: type 1 (CGB7) and type 2 (CGB3, -5, and -8). Here, we demonstrated in situ and ex vivo on placental villi and in vitro in primary cultures of human cytotrophoblasts that type 1 and 2 β-hCG RNAs and proteins were expressed by trophoblasts and that these expressions were higher before blood enters in the intervillous space (8-9 vs. 12-14 WA). hCG was immunodetected in villous mononucleated cytotrophoblasts (VCT) and syncytiotrophoblast (ST) at 8-9 WA but only in ST at 12-14 WA. Furthermore, hCG secretion was fourfold higher in VCT cultures from 8-9 WA compared with 12-14 WA. Interestingly, VCT from 8-9 WA placentas were found to exhibit more fusion features. Taken together, we showed that type 1 and type 2 β-hCG are highly expressed by VCT in the early first trimester, contributing to the high levels of hCG found in maternal serum at this term.

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.