Oxygen and trophoblast biology - a source of controversy. Placenta 32(Suppl 2):S109-S118

Department of Obstetrics and Gynecology, Washington University School of Medicine, St Louis, MO 63110, USA.
Placenta (Impact Factor: 2.71). 03/2011; 32 Suppl 2(2):S109-18. DOI: 10.1016/j.placenta.2010.12.013
Source: PubMed


Oxygen is necessary for life yet too much or too little oxygen is toxic to cells. The oxygen tension in the maternal plasma bathing placental villi is <20 mm Hg until 10-12 weeks' gestation, rising to 40-80 mm Hg and remaining in this range throughout the second and third trimesters. Maldevelopment of the maternal spiral arteries in the first trimester predisposes to placental dysfunction and sub-optimal pregnancy outcomes in the second half of pregnancy. Although low oxygen at the site of early placental development is the norm, controversy is intense when investigators interpret how defective transformation of spiral arteries leads to placental dysfunction during the second and third trimesters. Moreover, debate rages as to what oxygen concentrations should be considered normal and abnormal for use in vitro to model villous responses in vivo. The placenta may be injured in the second half of pregnancy by hypoxia, but recent evidence shows that ischemia with reoxygenation and mechanical damage due to high flow contributes to the placental dysfunction of diverse pregnancy disorders. We overview normal and pathologic development of the placenta, consider variables that influence experiments in vitro, and discuss the hotly debated question of what in vitro oxygen percentage reflects the normal and abnormal oxygen concentrations that occur in vivo. We then describe our studies that show cultured villous trophoblasts undergo apoptosis and autophagy with phenotype-related differences in response to hypoxia.

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Available from: Mark S. Longtine, Jan 16, 2015
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    • "Early identification of at risk pregnancies can improve outcomes through early intervention and improved monitoring of the pregnancy. While symptoms often do not present until late in pregnancy, defective trophoblast invasion in the first trimester is a primary insult in the development of preeclampsia [2]. This leads to reduced oxygen tension in the placenta and subsequently, altered trophoblast development, reoxygenation stress, and increased shedding of syncytiotrophoblast particles into the mother's blood. "
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    ABSTRACT: Maternal preeclampsia is associated with altered placental development in the first trimester of pregnancy. Confined placental trisomy 16 mosaicism (CPM16) is a genetic abnormality of the placenta that is highly predisposing to preeclampsia. We previously demonstrated widespread alterations in DNA methylation in 3rd trimester placentae associated with chromosomally normal early-onset preeclampsia (EOPET) and questioned whether similar changes would be associated with CPM16, making this condition a potential model for studying EOPET-associated changes early in pregnancy. Using the Illumina Infinium HumanMethylation450 BeadChip, 3rd trimester CPM16 placental samples (N = 10) were compared to gestational age matched controls, and to 1st trimester trisomy 16 placentae (N = 5). DNA methylation differences associated with CPM16 were identified at 2254 CpGs using stringent criteria (FDR < 0.01, Δβ > 0.15). A subset of these differences (11%; p < 0.0001) overlapped those observed in chromosomally normal EOPET using similarly stringent criteria (FDR < 0.01; Δβ > 0.125). Importantly, the majority of EOPET-associated CpGs were significantly altered (p < 0.05) in CPM16 with a similar Δβ distribution. This was true for CPM16 with (N = 5) and without (N = 5) EOPET, although EOPET cases showed a tendency towards larger changes. Of the shared CPM16/EOPET associated changes, three CpGs near two genes (ARGHEF37 and JUNB) were also altered in 1st trimester trisomy 16 placentae. Despite the limited sample size, widespread DNA methylation changes are observed in Trisomy 16 that overlap those seen previously in chromosomally normal EOPET. Hence, Trisomy 16 may provide a model to study the progression of placental changes that occurs in EOPET across different gestational ages.
    Full-text · Article · Jan 2014 · Placenta
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    • "Villous trophoblasts are composed of cytotrophoblasts and syncytiotrophoblasts. During intact placentation, the placenta is constructed under low oxygen (2–5% O2) and low glucose concentrations (1 mM) until 11 weeks of gestation [1], [2], [3], [4]. Intra-placental oxygen tension is rapidly increased after 12 weeks because endovascular EVTs invade the uterine spiral arteries, replace endothelial cells, and participate in the degradation of tunica media smooth muscle cells [5]. "
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    ABSTRACT: Extravillous trophoblasts (EVTs) characterize the invasion of the maternal decidua under low oxygen and poor nutrition at the early feto-maternal interface to establish a successful pregnancy. We previously reported that autophagy in EVTs was activated under 2% O2 in vitro, and autophagy activation was also observed in EVTs at the early feto-maternal interface in vivo. Here, we show that autophagy is an energy source for the invasion of EVTs. Cobalt chloride (CoCl2), which induces hypoxia inducible factor 1α (HIF1α) overexpression, activated autophagy in HTR8/SVneo cells, an EVT cell line. The number of invading HTR8-ATG4BC74A cells, an autophagy-deficient EVT cell line, was markedly reduced by 81 percent with the CoCl2 treatment through the suppression of MMP9 level, although CoCl2 did not affect the cellular invasion of HTR8-mStrawberry cells, a control cell line. HTR8-ATG4BC74A cells treated with CoCl2 showed a decrease in cellular adenosine triphosphate (ATP) levels and a compensatory increase in the expression of purinergic receptor P2X ligand-gated ion channel 7 (P2RX7), which is stimulated with ATP, whereas HTR8-mStrawberry cells maintained cellular ATP levels and did not affect P2RX7 expression. Furthermore, the decreased invasiveness of HTR8-ATG4BC74A cells treated with CoCl2 was neutralized by ATP supplementation to the level of HTR8-ATG4BC74A cells treated without CoCl2. These results suggest that autophagy plays a role in maintaining homeostasis by countervailing HIF1α-mediated cellular energy consumption in EVTs.
    Preview · Article · Oct 2013 · PLoS ONE
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    • "Moreover, we observed similar pO2 and pCO2 levels in umbilical artery between groups; consequently, no differences in HIF-1α expression were found according to the mode of onset of labor. Hypoxia stabilizes HIF-1α, and HIF-1α is a major regulator of the cellular response to hypoxia [10]; moreover, hypoxia can induce autophagy [25–28]. Therefore, we speculated that similar levels of oxidative stress and hypoxia can be present in spontaneous and pharmacologically induced labor, although this hypothesis needs to be confirmed. "
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    ABSTRACT: Induction of labor is one of the most used procedures in obstetrics, performed to achieve vaginal delivery through cervical ripening and stimulation of uterine contractions. We investigated the impact of induction of labor upon placental autophagy, a catabolic pathway activated in response to alteration of the physiological intracellular conditions. We collected 28 singleton placentas at the time of uncomplicated term vaginal delivery (7 spontaneous onset of labor, 21 induced labor). Autophagy was evaluated by immunohistochemistry, immunofluorescence, and immunoblotting. No significant difference in the autophagy expression was found between spontaneous or induced onset of labor. We found an inverse relationship between autophagy expression and the maternal prepregnancy body mass index, irrespective of the mode of labor onset. This result could be related to the nutritional maternal habits before and throughout pregnancy rather than rapid metabolic changes during labor.
    Full-text · Article · Jul 2013
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