Altered cyclic AMP-dependent human chorionic gonadotropin production in cultured human placental trophoblasts exposed to ethanol

Transposable elements, placental development, and oocyte activation: Cellular stress and AMPK links jumping genes with the creation of human life

Transposable elements (TEs), also known as "jumping genes", are DNA sequences first described by Nobel laureate Barbara McClintock that comprise nearly half of the human genome and are able to transpose or move from one genomic location to another. As McClintock also noted that a genome "shock" or stress may induce TE activation and transposition, accumulating evidence suggests that cellular stress (e.g. mediated by increases in intracellular reactive oxygen species [ROS] and calcium [Ca2+], etc.) induces TE mobilization in several model organisms and L1s (a member of the retrotransposon class of TEs) are active and capable of retrotransposition in human oocytes, human sperm, and in human neural progenitor cells. Cellular stress also plays a critical role in human placental development, with cytotrophoblast (CTB) differentiation leading to the formation of the syncytiotrophoblast (STB), a cellular layer that facilitates nutrient and gas exchange between the mother and the fetus. Syncytin-1, a protein that promotes fusion of CTB cells and is necessary for STB formation, and its receptor is found in human sperm and human oocytes, respectively, and increases in ROS and Ca2+ promote trophoblast differentiation and syncytin-1 expression. Cellular stress is also essential in promoting human oocyte maturation and activation which, similar to TE mobilization, can be induced by compounds that increase intracellular Ca2+ and ROS levels. AMPK is a master metabolic regulator activated by increases in ROS, Ca2+, and/or an AMP(ADP)/ATP ratio increase, etc. as well as compounds that induce L1 mobilization in human cells. AMPK knockdown inhibits trophoblast differentiation and AMPK-activating compounds that promote L1 mobility also enhance trophoblast differentiation. Cellular stressors that induce TE mobilization (e.g. heat shock) also promote oocyte maturation in an AMPK-dependent manner and the antibiotic ionomycin activates AMPK, promotes TE activation, and induces human oocyte activation, producing normal, healthy children. Metformin promotes AMPK-dependent telomerase activation (critical for telomere maintenance) and induces activation of the endonuclease RAG1 (promotes DNA cleavage and transposition) via AMPK. Both RAG1 and telomerase are derived from TEs. It is our hypothesis that cellular stress and AMPK links TE activation and transposition with placental development and oocyte activation, facilitating both human genome evolution and the creation of all human life. We also propose the novel observation that various cellular stress-inducing compounds (e.g. metformin, resveratrol, etc.) may facilitate beneficial TE activation and transposition and enhance fertilization and embryological development through a common mechanism of AMPK activation.

Prenatal ethanol exposure and placental hCG and IGF2 expression

INTRODUCTION

Fetal alcohol spectrum disorder (FASD) is the main cause of preventable non-genetic mental retardation. Diagnosis of prenatal exposure to ethanol (PEE) is based on questionnaires and biomarkers in perinatal matrices. Early diagnosis of FASD is important to mitigate secondary disabilities that will arise later in life. It is important to identify biomarkers related to cellular damage caused by PEE. The main objective was to identify novel candidate biomarkers from placental tissue using an in vitro model of exposure to ethanol and to support it in placental tissue obtained from pregnancies with PEE assessed by fatty acid esters in meconium samples.

METHODS

First, hormone production was examined using two different human trophoblast cell lines, JEG3 and BeWo. Viable cell count by exclusion method was analyzed and human chorionic gonadotrophin (hCG) and insulin-like growth factor 2 (IGF2) were quantified by Western blot and ELISA. Second, these techniques were used in protein lysates from human placentas from pregnancies with and without exposure to ethanol.

RESULTS

Both trophoblast cell lines showed a decrease in cell viability accompanied with apoptosis activation after a chronic ethanol treatment. Moreover, we showed an increase in the secretion of hCG and IGF2 in a dose-dependent manner. Interestingly, this increase was also observed in a set of human placenta tissue from fetuses exposed prenatally to ethanol.

DISCUSSION

Ethanol exposure during pregnancy causes placenta cell damage, so altering its normal function. The specific hCG and IGF2 release pattern is a candidate surrogated biomarker of the damage due to PEE.

Ethanol cytotoxic effect on trophoblast cells

Prenatal ethanol exposure may cause both, altered fetal neurodevelopment and impaired placental function. These disturbances can lead to growth retardation, which is one of the most prevalent features in Fetal Alcohol Syndrome (FAS). It is not known whether there is a specific pattern of cytotoxicity caused by ethanol that can be extrapolated to other cell types. The aim of this study was to determine the cytotoxic effects caused by sustained exposure of trophoblast cells to ethanol. The cytotoxic effect of sustained exposure to standard doses of ethanol on an in vitro human trophoblast cell line, JEG3, was examined. Viable cell count by exclusion method, total protein concentration, lactate dehydrogenase (LDH) activity and activation of apoptotic markers (P-H2AX, caspase-3 and PARP-1) were determined. Sustained exposure to ethanol decreased viable cell count and total protein concentration. LDH activity did not increased in exposed cells but apoptotic markers were detected. In addition, there was a dose-dependent relationship between ethanol concentration and apoptotic pathways activation. Sustained ethanol exposure causes cellular cytotoxicity by apoptotic pathways induction as a result of DNA damage. This apoptotic induction may partially explain the altered function of placental cells and the damage previously detected in other tissues.

Adverse placental effect of formic acid on hCG secretion is mitigated by folic acid

AIMS

Formic acid has recently been detected in maternal blood and umbilical cord blood of infants born to alcohol abusing mothers. This toxic metabolite of methanol requires folate for detoxification. We hypothesized that formic acid produced in the maternal circulation will transfer across the placenta and will be toxic to the placenta. Our objectives were, first, to determine whether formic acid transfers across the human placenta and whether it is toxic to the placenta and second, to determine whether folate can decrease transplacental transfer of formic acid and mitigate toxicity.

METHODS

Dual perfusion of a single placental lobule ex vivo was used to characterize the transfer of formic acid across the placenta. After a 1-h control period, formic acid (2 mM) was introduced into the maternal circulation with (n = 4) or without folate (1 µM) (n = 4) and was allowed to equilibrate for 3 h.

RESULTS

Formic acid transferred rapidly from the maternal to the fetal circulation, and transfer was not altered with the addition of folate. Compared with the control period, there was a significant decrease in hCG secretion (P = 0.03) after addition of formic acid. The addition of folic acid to the perfusate mitigated the decrease in hCG.

CONCLUSIONS

Formic acid rapidly transfers across the placenta and thus has the potential to be toxic to the developing fetus. Formic acid decreases hCG secretion in the placenta, which may alter steroidogenesis and differentiation of the cytotrophoblasts, and this adverse effect can be mitigated by folate.

Ethanol and the placenta: A review

OBJECTIVE

In this paper we review published studies of alcohol exposure on placentation, placenta growth and function.

METHODS

We searched PubMed using the MeSH terms: placenta, ethanol, fetal alcohol syndrome and prenatal exposure with delayed effects. We searched the years 1996-2006 and used the references from other articles to expand our search. We limited the search to English only and human only. We excluded studies using choriocarcinoma and animal studies. We grouped the 66 papers into seven topic areas for ease of review.

RESULTS

Alcohol exposure is associated with placental dysfunction, decreased placental size, impaired blood flow and nutrient transport, endocrine changes, increased rates of stillbirth and abruption, umbilical cord vasoconstriction, and low birth weight.

CONCLUSIONS

Prenatal alcohol exposure has a broad range of adverse effects on placental development and function. Additional research on placental development from populations with heavy alcohol exposure should be encouraged. A tissue bank of placentas with detailed assessment of exposure to alcohol, smoking and other relevant data should be considered as a repository to support additional research.